diff --git a/internal/repository/energy_repo.go b/internal/repository/energy_repo.go
index 2d7ffac..55c0d7f 100644
--- a/internal/repository/energy_repo.go
+++ b/internal/repository/energy_repo.go
@@ -12,7 +12,8 @@ import (
 
 // EnergyRepo 域能数据访问
 type EnergyRepo struct {
-	db *gorm.DB
+	db        *gorm.DB
+	fundStore service.FundStore // 用于 Transaction 时创建事务范围的 FundStore
 }
 
 // NewEnergyRepo 构造函数
@@ -20,11 +21,28 @@ func NewEnergyRepo(db *gorm.DB) *EnergyRepo {
 	return &EnergyRepo{db: db}
 }
 
+// SetFundStore 设置公户仓储引用（用于跨仓库事务）
+func (r *EnergyRepo) SetFundStore(s service.FundStore) {
+	r.fundStore = s
+}
+
 // WithTx 基于给定事务连接创建新的 EnergyRepo（确保事务内操作原子性）
 func (r *EnergyRepo) WithTx(tx *gorm.DB) service.EnergyStore {
 	return &EnergyRepo{db: tx}
 }
 
+// Transaction 在事务内执行业务逻辑，自动管理 EnergyStore 和 FundStore 的事务范围
+func (r *EnergyRepo) Transaction(fn func(txEnergy service.EnergyStore, txFund service.FundStore) error) error {
+	return r.db.Transaction(func(tx *gorm.DB) error {
+		txEnergy := r.WithTx(tx)
+		var txFund service.FundStore
+		if r.fundStore != nil {
+			txFund = r.fundStore.WithTx(tx)
+		}
+		return fn(txEnergy, txFund)
+	})
+}
+
 // FindUserByID 查找用户（获取能量余额等）
 func (r *EnergyRepo) FindUserByID(userID uint) (*model.User, error) {
 	var user model.User
diff --git a/internal/repository/favorite_repo.go b/internal/repository/favorite_repo.go
index c3b879c..fb8c6b5 100644
--- a/internal/repository/favorite_repo.go
+++ b/internal/repository/favorite_repo.go
@@ -22,6 +22,13 @@ func (r *FavoriteRepo) WithTx(tx *gorm.DB) service.FavoriteStore {
 	return &FavoriteRepo{db: tx}
 }
 
+// Transaction 在事务内执行业务逻辑
+func (r *FavoriteRepo) Transaction(fn func(tx service.FavoriteStore) error) error {
+	return r.db.Transaction(func(tx *gorm.DB) error {
+		return fn(r.WithTx(tx))
+	})
+}
+
 // ======================== Folder CRUD ========================
 
 // CreateFolder 创建收藏夹
diff --git a/internal/repository/follow_repo.go b/internal/repository/follow_repo.go
index 9bc615b..d8fd04c 100644
--- a/internal/repository/follow_repo.go
+++ b/internal/repository/follow_repo.go
@@ -22,6 +22,13 @@ func (r *FollowRepo) WithTx(tx *gorm.DB) service.FollowStore {
 	return &FollowRepo{db: tx}
 }
 
+// Transaction 在事务内执行业务逻辑
+func (r *FollowRepo) Transaction(fn func(tx service.FollowStore) error) error {
+	return r.db.Transaction(func(tx *gorm.DB) error {
+		return fn(r.WithTx(tx))
+	})
+}
+
 // Create 创建关注
 func (r *FollowRepo) Create(follow *model.UserFollow) error {
 	return r.db.Create(follow).Error
diff --git a/internal/repository/reaction_repo.go b/internal/repository/reaction_repo.go
index 6510b98..372f61c 100644
--- a/internal/repository/reaction_repo.go
+++ b/internal/repository/reaction_repo.go
@@ -22,6 +22,22 @@ func (r *ReactionRepo) WithTx(tx *gorm.DB) service.ReactionStore {
 	return &ReactionRepo{db: tx}
 }
 
+// Transaction 在事务内执行业务逻辑
+func (r *ReactionRepo) Transaction(fn func(tx service.ReactionStore) error) error {
+	return r.db.Transaction(func(tx *gorm.DB) error {
+		return fn(r.WithTx(tx))
+	})
+}
+
+// GetPostLikesCount 查询文章点赞数
+func (r *ReactionRepo) GetPostLikesCount(postID uint) (int, error) {
+	var post model.Post
+	if err := r.db.Select("likes_count").First(&post, postID).Error; err != nil {
+		return 0, err
+	}
+	return post.LikesCount, nil
+}
+
 // FindLike 查找点赞记录
 func (r *ReactionRepo) FindLike(userID, postID uint) (*model.PostLike, error) {
 	var like model.PostLike
diff --git a/internal/router/deps_extra.go b/internal/router/deps_extra.go
index ecf6caf..8a85c62 100644
--- a/internal/router/deps_extra.go
+++ b/internal/router/deps_extra.go
@@ -22,8 +22,9 @@ func buildDeps(db *gorm.DB, cfg *config.Config, siteSettings *config.SiteSetting
 	// 域能系统
 	energyRepo := repository.NewEnergyRepo(db)
 	fundRepo := repository.NewFundRepo(db)
-	energyService := service.NewEnergyService(db, energyRepo, nil, notificationService)
-	energyService.SetFundRepo(fundRepo)
+	energyRepo.SetFundStore(fundRepo) // 为跨仓库 Transaction 注入 FundStore
+	energyService := service.NewEnergyService(energyRepo, nil, notificationService)
+	energyService.SetFundRepo(fundRepo) // 只读查询
 
 	// 等级/签到/任务系统（链式注入域能服务）
 	_, levelSvc, levelCtrl := buildDepsLevel(db, notificationService, authMdw)
@@ -72,18 +73,18 @@ func buildDeps(db *gorm.DB, cfg *config.Config, siteSettings *config.SiteSetting
 
 	// 赞/踩系统
 	reactionRepo := repository.NewReactionRepo(db)
-	reactionService := service.NewReactionService(db, reactionRepo)
+	reactionService := service.NewReactionService(reactionRepo)
 	reactionCtrl := controller.NewReactionController(reactionService)
 
 	// 关注系统
 	followRepo := repository.NewFollowRepo(db)
-	followService := service.NewFollowService(db, followRepo)
+	followService := service.NewFollowService(followRepo)
 	followService.SetNotifier(notificationService) // 关注通知
 	followCtrl := controller.NewFollowController(followService)
 
 	// 收藏夹系统（需在 SpaceController 之前初始化）
 	favoriteRepo := repository.NewFavoriteRepo(db)
-	favoriteService := service.NewFavoriteService(db, favoriteRepo)
+	favoriteService := service.NewFavoriteService(favoriteRepo)
 	favoriteCtrl := controller.NewFavoriteController(favoriteService)
 
 	// 用户空间
diff --git a/internal/service/energy_admin.go b/internal/service/energy_admin.go
index 684ba57..75cb51c 100644
--- a/internal/service/energy_admin.go
+++ b/internal/service/energy_admin.go
@@ -5,8 +5,6 @@ import (
 
 	"metazone.cc/metalab/internal/common"
 	"metazone.cc/metalab/internal/model"
-
-	"gorm.io/gorm"
 )
 
 // AdminAdjust 后台调整用户域能
@@ -16,13 +14,10 @@ func (s *EnergyService) AdminAdjust(operatorUID uint, userIDs []uint, amount int
 		mode = model.FundTypeAdminTransfer
 	}
 
-	return s.db.Transaction(func(tx *gorm.DB) error {
-		txRepo := s.repo.WithTx(tx)
-
+	return s.repo.Transaction(func(txRepo EnergyStore, txFundRepo FundStore) error {
 		// admin_transfer：公户出账需检查余额（行锁防 TOCTOU 竞态）
 		isAdminTransfer := mode == model.FundTypeAdminTransfer
-		if isAdminTransfer && amount > 0 && s.fundRepo != nil {
-			txFundRepo := s.fundRepo.WithTx(tx)
+		if isAdminTransfer && amount > 0 && txFundRepo != nil {
 			totalCost := amount * len(userIDs)
 			balance, err := txFundRepo.LockAndGetBalance()
 			if err != nil {
@@ -52,8 +47,7 @@ func (s *EnergyService) AdminAdjust(operatorUID uint, userIDs []uint, amount int
 		}
 
 		// admin_transfer：公户扣款 + 公户流水（system_operation 不碰公户）
-		if isAdminTransfer && s.fundRepo != nil {
-			txFundRepo := s.fundRepo.WithTx(tx)
+		if isAdminTransfer && txFundRepo != nil {
 			totalCost := amount * len(userIDs)
 			if err := txFundRepo.IncrBalance(-totalCost); err != nil {
 				return fmt.Errorf("公户余额调整失败: %w", err)
diff --git a/internal/service/energy_energize.go b/internal/service/energy_energize.go
index 1b6c2c2..19ca1bd 100644
--- a/internal/service/energy_energize.go
+++ b/internal/service/energy_energize.go
@@ -6,8 +6,6 @@ import (
 
 	"metazone.cc/metalab/internal/common"
 	"metazone.cc/metalab/internal/model"
-
-	"gorm.io/gorm"
 )
 
 // Energize 赋能文章
@@ -23,19 +21,10 @@ func (s *EnergyService) Energize(energizerID uint, postID uint, amount int) (int
 	var expToday time.Time
 	var expTotal int
 
-	err := s.db.Transaction(func(tx *gorm.DB) error {
-		txRepo := s.repo.WithTx(tx)
-		var txFundRepo FundStore
-		if s.fundRepo != nil {
-			txFundRepo = s.fundRepo.WithTx(tx)
-		}
-
+	err := s.repo.Transaction(func(txRepo EnergyStore, txFundRepo FundStore) error {
 		// 1. 检查帖子存在，获取作者
 		post, err := txRepo.FindPostByID(postID)
 		if err != nil {
-			if err == gorm.ErrRecordNotFound {
-				return common.ErrPostNotFound
-			}
 			return fmt.Errorf("查询帖子失败: %w", err)
 		}
 
diff --git a/internal/service/energy_operations.go b/internal/service/energy_operations.go
index e57b4a8..c2cac5a 100644
--- a/internal/service/energy_operations.go
+++ b/internal/service/energy_operations.go
@@ -5,8 +5,6 @@ import (
 
 	"metazone.cc/metalab/internal/common"
 	"metazone.cc/metalab/internal/model"
-
-	"gorm.io/gorm"
 )
 
 // CheckInEnergy 签到获得域能（LV0 用户不调用此方法）
@@ -27,9 +25,7 @@ func (s *EnergyService) CheckInEnergy(userID uint) error {
 // DeductOnRename 改名扣域能（首次改名免费，不调用此方法）
 // 事务包裹：扣用户域能 + 入公户 + 写流水
 func (s *EnergyService) DeductOnRename(userID uint) error {
-	return s.db.Transaction(func(tx *gorm.DB) error {
-		txRepo := s.repo.WithTx(tx)
-
+	return s.repo.Transaction(func(txRepo EnergyStore, txFundRepo FundStore) error {
 		// 检查域能余额（非 owner 需 ≥ 0）
 		user, err := txRepo.FindUserByID(userID)
 		if err != nil {
@@ -44,8 +40,7 @@ func (s *EnergyService) DeductOnRename(userID uint) error {
 		}
 
 		// 公户入账
-		if s.fundRepo != nil {
-			txFundRepo := s.fundRepo.WithTx(tx)
+		if txFundRepo != nil {
 			if err := txFundRepo.IncrBalance(-EnergyRename); err != nil { // EnergyRename = -60，入公户 +60
 				return fmt.Errorf("公户入账失败: %w", err)
 			}
@@ -73,12 +68,9 @@ func (s *EnergyService) DeductOnRename(userID uint) error {
 
 // RefundOnRenameReject 改名审核被拒，从公户返还域能
 func (s *EnergyService) RefundOnRenameReject(userID uint) error {
-	return s.db.Transaction(func(tx *gorm.DB) error {
-		txRepo := s.repo.WithTx(tx)
-
+	return s.repo.Transaction(func(txRepo EnergyStore, txFundRepo FundStore) error {
 		// 从公户支出（允许透支）
-		if s.fundRepo != nil {
-			txFundRepo := s.fundRepo.WithTx(tx)
+		if txFundRepo != nil {
 			if err := txFundRepo.IncrBalance(-EnergyRenameRefund); err != nil {
 				return fmt.Errorf("公户出账失败: %w", err)
 			}
@@ -111,16 +103,13 @@ func (s *EnergyService) RefundOnRenameReject(userID uint) error {
 // DeductOnDeletePost 删稿扣域能（扣文章作者的域能，无视负数）
 // 事务包裹：扣用户域能 + 入公户 + 写流水
 func (s *EnergyService) DeductOnDeletePost(authorUserID uint, postID uint) error {
-	return s.db.Transaction(func(tx *gorm.DB) error {
-		txRepo := s.repo.WithTx(tx)
-
+	return s.repo.Transaction(func(txRepo EnergyStore, txFundRepo FundStore) error {
 		if err := txRepo.AddEnergy(authorUserID, EnergyDeletePost); err != nil {
 			return fmt.Errorf("扣减删稿域能失败: %w", err)
 		}
 
 		// 公户入账
-		if s.fundRepo != nil {
-			txFundRepo := s.fundRepo.WithTx(tx)
+		if txFundRepo != nil {
 			if err := txFundRepo.IncrBalance(-EnergyDeletePost); err != nil { // EnergyDeletePost = -20，入公户 +20
 				return fmt.Errorf("公户入账失败: %w", err)
 			}
diff --git a/internal/service/energy_service.go b/internal/service/energy_service.go
index e94afdf..29880db 100644
--- a/internal/service/energy_service.go
+++ b/internal/service/energy_service.go
@@ -1,9 +1,5 @@
 package service
 
-import (
-	"gorm.io/gorm"
-)
-
 // expAdder EnergyService 对经验增加的最小依赖（ISP）
 type expAdder interface {
 	AddExp(userID uint, delta int) (newExp int, levelUp bool, err error)
@@ -11,16 +7,15 @@ type expAdder interface {
 
 // EnergyService 域能业务逻辑
 type EnergyService struct {
-	db       *gorm.DB
 	repo     EnergyStore
-	fundRepo FundStore
+	fundRepo FundStore // 只读查询用（GetFundBalance/GetFundLogs）
 	expSvc   expAdder
 	notifSvc energyNotifier
 }
 
 // NewEnergyService 构造函数
-func NewEnergyService(db *gorm.DB, repo EnergyStore, expSvc expAdder, notifSvc energyNotifier) *EnergyService {
-	return &EnergyService{db: db, repo: repo, expSvc: expSvc, notifSvc: notifSvc}
+func NewEnergyService(repo EnergyStore, expSvc expAdder, notifSvc energyNotifier) *EnergyService {
+	return &EnergyService{repo: repo, expSvc: expSvc, notifSvc: notifSvc}
 }
 
 // SetExpAdder 链式注入经验服务（用于赋能获得经验）
@@ -28,7 +23,7 @@ func (s *EnergyService) SetExpAdder(svc expAdder) {
 	s.expSvc = svc
 }
 
-// SetFundRepo 链式注入公户仓储
+// SetFundRepo 链式注入公户仓储（只读查询）
 func (s *EnergyService) SetFundRepo(repo FundStore) {
 	s.fundRepo = repo
 }
diff --git a/internal/service/favorite_items.go b/internal/service/favorite_items.go
index a0382e0..bf6c4da 100644
--- a/internal/service/favorite_items.go
+++ b/internal/service/favorite_items.go
@@ -5,8 +5,6 @@ import (
 
 	"metazone.cc/metalab/internal/common"
 	"metazone.cc/metalab/internal/model"
-
-	"gorm.io/gorm"
 )
 
 // AddToFolder 将文章加入收藏夹（会先移除该文章在其他收藏夹的收藏）
@@ -20,8 +18,7 @@ func (s *FavoriteService) AddToFolder(userID, folderID, postID uint) error {
 		return common.ErrPermissionDenied
 	}
 
-	return s.db.Transaction(func(tx *gorm.DB) error {
-		txRepo := s.repo.WithTx(tx)
+	return s.repo.Transaction(func(txRepo FavoriteStore) error {
 
 		// 如果该文章已在其他收藏夹中，先移除
 		existing, err := txRepo.FindItemByUserAndPost(userID, postID)
@@ -60,8 +57,7 @@ func (s *FavoriteService) RemoveFromFolder(userID, folderID, postID uint) error
 		return common.ErrPermissionDenied
 	}
 
-	return s.db.Transaction(func(tx *gorm.DB) error {
-		txRepo := s.repo.WithTx(tx)
+	return s.repo.Transaction(func(txRepo FavoriteStore) error {
 		if err := txRepo.DeleteItem(folderID, postID); err != nil {
 			return fmt.Errorf("移除收藏: %w", err)
 		}
diff --git a/internal/service/favorite_service.go b/internal/service/favorite_service.go
index 5265e56..b468ea6 100644
--- a/internal/service/favorite_service.go
+++ b/internal/service/favorite_service.go
@@ -32,6 +32,8 @@ type FavoriteStore interface {
 	AggregateFavoritesByAuthor(userID uint, since string) ([]TrendPoint, error)
 	// Tx
 	WithTx(tx *gorm.DB) FavoriteStore
+	// Transaction 在事务内执行业务逻辑，自动管理 WithTx
+	Transaction(fn func(tx FavoriteStore) error) error
 }
 
 // FavoriteListResult 收藏夹列表 + 收藏内容
@@ -56,13 +58,12 @@ type FavoriteStatus struct {
 
 // FavoriteService 收藏夹业务逻辑
 type FavoriteService struct {
-	db   *gorm.DB
 	repo FavoriteStore
 }
 
 // NewFavoriteService 构造函数
-func NewFavoriteService(db *gorm.DB, repo FavoriteStore) *FavoriteService {
-	return &FavoriteService{db: db, repo: repo}
+func NewFavoriteService(repo FavoriteStore) *FavoriteService {
+	return &FavoriteService{repo: repo}
 }
 
 // ensureDefaultFolder 确保用户有默认收藏夹（不存在则创建）
@@ -187,9 +188,7 @@ func (s *FavoriteService) DeleteFolder(userID, folderID uint) error {
 		return fmt.Errorf("默认收藏夹不可删除")
 	}
 
-	return s.db.Transaction(func(tx *gorm.DB) error {
-		txRepo := s.repo.WithTx(tx)
-
+	return s.repo.Transaction(func(txRepo FavoriteStore) error {
 		// 先清理 items 的 fans 计数
 		items, _, _ := txRepo.ListItemsByFolder(folderID, 0, 10000)
 		for _, item := range items {
diff --git a/internal/service/follow_service.go b/internal/service/follow_service.go
index e029916..706dbf9 100644
--- a/internal/service/follow_service.go
+++ b/internal/service/follow_service.go
@@ -6,8 +6,6 @@ import (
 
 	"metazone.cc/metalab/internal/common"
 	"metazone.cc/metalab/internal/model"
-
-	"gorm.io/gorm"
 )
 
 // FollowStatus 关注关系状态
@@ -33,14 +31,13 @@ type followNotifier interface {
 
 // FollowService 关注业务逻辑
 type FollowService struct {
-	db       *gorm.DB
 	repo     FollowStore
 	notifier followNotifier
 }
 
 // NewFollowService 构造函数
-func NewFollowService(db *gorm.DB, repo FollowStore) *FollowService {
-	return &FollowService{db: db, repo: repo}
+func NewFollowService(repo FollowStore) *FollowService {
+	return &FollowService{repo: repo}
 }
 
 // SetNotifier 注入通知服务
@@ -55,9 +52,7 @@ func (s *FollowService) Toggle(followerID, followeeID uint) (bool, error) {
 	}
 
 	var isFollowing bool
-	err := s.db.Transaction(func(tx *gorm.DB) error {
-		txRepo := s.repo.WithTx(tx)
-
+	err := s.repo.Transaction(func(txRepo FollowStore) error {
 		exists, err := txRepo.Exists(followerID, followeeID)
 		if err != nil {
 			return fmt.Errorf("查询关注状态失败: %w", err)
diff --git a/internal/service/reaction_service.go b/internal/service/reaction_service.go
index ca5bffd..526c2e9 100644
--- a/internal/service/reaction_service.go
+++ b/internal/service/reaction_service.go
@@ -4,10 +4,7 @@ import (
 	"fmt"
 	"time"
 
-	"metazone.cc/metalab/internal/common"
 	"metazone.cc/metalab/internal/model"
-
-	"gorm.io/gorm"
 )
 
 // ReactionType 反应类型
@@ -21,13 +18,12 @@ const (
 
 // ReactionService 赞/踩业务逻辑
 type ReactionService struct {
-	db   *gorm.DB
 	repo ReactionStore
 }
 
 // NewReactionService 构造函数
-func NewReactionService(db *gorm.DB, repo ReactionStore) *ReactionService {
-	return &ReactionService{db: db, repo: repo}
+func NewReactionService(repo ReactionStore) *ReactionService {
+	return &ReactionService{repo: repo}
 }
 
 // ToggleLike 切换点赞（含踩互斥逻辑）
@@ -35,9 +31,7 @@ func NewReactionService(db *gorm.DB, repo ReactionStore) *ReactionService {
 func (s *ReactionService) ToggleLike(userID, postID uint) (bool, error) {
 	var isLiked bool
 
-	err := s.db.Transaction(func(tx *gorm.DB) error {
-		txRepo := s.repo.WithTx(tx)
-
+	err := s.repo.Transaction(func(txRepo ReactionStore) error {
 		// 查当前状态
 		_, likeErr := txRepo.FindLike(userID, postID)
 		hasLike := likeErr == nil
@@ -104,9 +98,7 @@ func (s *ReactionService) recordLikeForAggregation(postID uint, likerID uint) {
 func (s *ReactionService) ToggleDislike(userID, postID uint) (bool, error) {
 	var isDisliked bool
 
-	err := s.db.Transaction(func(tx *gorm.DB) error {
-		txRepo := s.repo.WithTx(tx)
-
+	err := s.repo.Transaction(func(txRepo ReactionStore) error {
 		// 查当前状态
 		_, likeErr := txRepo.FindLike(userID, postID)
 		hasLike := likeErr == nil
@@ -165,12 +157,9 @@ func (s *ReactionService) GetReaction(userID, postID uint) (ReactionType, error)
 
 // GetPostLikesCount 查询文章点赞数（公开展示）
 func (s *ReactionService) GetPostLikesCount(postID uint) (int, error) {
-	var post model.Post
-	if err := s.db.Select("likes_count").First(&post, postID).Error; err != nil {
-		if err == gorm.ErrRecordNotFound {
-			return 0, common.ErrPostNotFound
-		}
-		return 0, fmt.Errorf("查询文章失败: %w", err)
+	count, err := s.repo.GetPostLikesCount(postID)
+	if err != nil {
+		return 0, fmt.Errorf("查询文章点赞数: %w", err)
 	}
-	return post.LikesCount, nil
+	return count, nil
 }
diff --git a/internal/service/repository.go b/internal/service/repository.go
index d0ab248..401518f 100644
--- a/internal/service/repository.go
+++ b/internal/service/repository.go
@@ -113,6 +113,8 @@ type EnergyStore interface {
 	ListAllEnergyLogs(energyType string, offset, limit int) ([]model.EnergyLog, int64, error)
 	// WithTx 基于给定事务连接创建新的 EnergyStore（确保事务内操作原子性）
 	WithTx(tx *gorm.DB) EnergyStore
+	// Transaction 在事务内执行业务逻辑，自动管理 WithTx 和 FundStore 的事务范围
+	Transaction(fn func(txEnergy EnergyStore, txFund FundStore) error) error
 }
 
 // energyStore 向后兼容别名
@@ -172,10 +174,13 @@ type ReactionStore interface {
 	IncrPostLikes(postID uint, delta int) error
 	IncrPostDislikes(postID uint, delta int) error
 	GetPostAuthorID(postID uint) (uint, error)
+	GetPostLikesCount(postID uint) (int, error)
 	UpsertDailyLikeSummary(authorUID uint, date string, likerUID string) error
 	GetUnnotifiedSummaries(userID uint) ([]model.DailyLikeSummary, error)
 	MarkSummaryNotified(id uint) error
 	WithTx(tx *gorm.DB) ReactionStore
+	// Transaction 在事务内执行业务逻辑，自动管理 WithTx
+	Transaction(fn func(tx ReactionStore) error) error
 }
 
 // FollowStore FollowService 所需的最小仓储接口（ISP）
@@ -191,6 +196,8 @@ type FollowStore interface {
 	IncrFollowingCount(userID uint, delta int) error
 	GetFollowListPublic(userID uint) (bool, error)
 	WithTx(tx *gorm.DB) FollowStore
+	// Transaction 在事务内执行业务逻辑，自动管理 WithTx
+	Transaction(fn func(tx FollowStore) error) error
 }
 
 // TrendPoint 趋势数据点