feat: 实现关注系统 + 通知侧边栏分类 TAB + 点赞聚合通知

- 新增关注系统：UserFollow 模型、FollowService（toggle/status/列表隐私控制）
- User 新增 FollowersCount/FollowingCount/FollowListPublic/NotifyPrefs 字段
- Space 页面增加四态关注按钮（关注/已关注/回关/已互粉）+ 粉丝/关注数链接
- 新增 /space/:uid/followers 和 /space/:uid/following 列表页
- 新增 NotifyFollow/NotifyLikeAggregated 通知类型
- ReactionService 点赞时写入 daily_like_summary，访问时生成聚合通知
- FollowService 关注时触发 NotifyFollow 通知
- 消息中心侧边栏升级为分类 TAB（全部/系统通知/@艾特/点赞/关注）
- NotificationService 新增 ListByCategory 按分类分页查询

internal/service/notification_service.go

@@ -1,6 +1,9 @@
 package service
 
 import (
+	"fmt"
+	"sort"
+
 	"metazone.cc/metalab/internal/common"
 	"metazone.cc/metalab/internal/model"
 )
@@ -9,10 +12,16 @@ import (
 type notifRepo interface {
 	Create(n *model.Notification) error
 	ListByUser(userID uint, offset, limit int) ([]model.Notification, error)
+	ListByUserAndType(userID uint, notifyType string, offset, limit int) ([]model.Notification, error)
 	CountByUser(userID uint) (int64, error)
+	CountByUserAndType(userID uint, notifyType string) (int64, error)
 	CountUnread(userID uint) (int64, error)
+	CountUnreadByType(userID uint, notifyType string) (int64, error)
 	MarkRead(id, userID uint) error
 	MarkAllRead(userID uint) error
+	GetUnnotifiedDailyLikeSummaries(userID uint) ([]model.DailyLikeSummary, error)
+	MarkDailyLikeSummaryNotified(id uint) error
+	GetUsernameByID(userID uint) (string, error)
 }
 
 // NotificationService 消息/通知业务逻辑
@@ -39,8 +48,11 @@ func (s *NotificationService) Create(userID uint, notifyType, title, content str
 	return s.repo.Create(n)
 }
 
-// List 分页查询用户消息列表
+// List 分页查询用户消息列表（触发聚合通知检查）
 func (s *NotificationService) List(userID uint, page, pageSize int) (*model.NotificationListResult, error) {
+	// 自动触发点赞聚合通知生成
+	s.checkAndNotifyAggregation(userID)
+
 	p := common.Pagination{Page: page, PageSize: pageSize}
 	p.DefaultPagination()
 
@@ -69,6 +81,123 @@ func (s *NotificationService) List(userID uint, page, pageSize int) (*model.Noti
 	}, nil
 }
 
+// ListByCategory 按通知分类分页查询（供消息页分类 TAB 使用）
+func (s *NotificationService) ListByCategory(userID uint, category string, page, pageSize int) (*model.NotificationListResult, error) {
+	s.checkAndNotifyAggregation(userID)
+
+	p := common.Pagination{Page: page, PageSize: pageSize}
+	p.DefaultPagination()
+
+	// 分类→通知类型映射
+	notifyTypes := categoryTypes(category)
+	var combinedItems []model.Notification
+	var total int64
+
+	for _, nt := range notifyTypes {
+		c, _ := s.repo.CountByUserAndType(userID, nt)
+		total += c
+	}
+
+	allItems := make([]model.Notification, 0)
+	for _, nt := range notifyTypes {
+		items, err := s.repo.ListByUserAndType(userID, nt, 0, 10000) // 大 limit，在内存里分页
+		if err != nil {
+			continue
+		}
+		allItems = append(allItems, items...)
+	}
+
+	// 按 created_at 降序排序
+	sortNotifications(allItems)
+
+	// 分页
+	start := p.Offset()
+	end := start + p.PageSize
+	if start > len(allItems) {
+		start = len(allItems)
+	}
+	if end > len(allItems) {
+		end = len(allItems)
+	}
+	if start < end {
+		combinedItems = allItems[start:end]
+	}
+
+	if combinedItems == nil {
+		combinedItems = []model.Notification{}
+	}
+
+	totalPages := int((total + int64(p.PageSize) - 1) / int64(p.PageSize))
+	unread, _ := s.CountUnread(userID)
+
+	return &model.NotificationListResult{
+		Items:      combinedItems,
+		Total:      total,
+		Page:       p.Page,
+		TotalPages: totalPages,
+		Unread:     unread,
+	}, nil
+}
+
+// checkAndNotifyAggregation 检查并生成点赞聚合通知
+func (s *NotificationService) checkAndNotifyAggregation(userID uint) {
+	summaries, err := s.repo.GetUnnotifiedDailyLikeSummaries(userID)
+	if err != nil || len(summaries) == 0 {
+		return
+	}
+
+	for _, sm := range summaries {
+		count := countUIDs(sm.LikerUIDs)
+		var content string
+		if count <= 3 {
+			content = fmt.Sprintf("你的文章被 %d 人点赞了", count)
+		} else {
+			content = fmt.Sprintf("你的文章被 %d 人点赞了", count)
+		}
+		_ = s.Create(userID, model.NotifyLikeAggregated,
+			"点赞汇总通知",
+			content,
+			nil, nil)
+		_ = s.repo.MarkDailyLikeSummaryNotified(sm.ID)
+	}
+}
+
+func countUIDs(uids string) int {
+	if uids == "" {
+		return 0
+	}
+	count := 1
+	for _, c := range uids {
+		if c == ',' {
+			count++
+		}
+	}
+	return count
+}
+
+// categoryTypes 分类→通知类型列表
+func categoryTypes(category string) []string {
+	switch category {
+	case "system":
+		return []string{model.NotifyAuditApproved, model.NotifyAuditRejected, model.NotifyPostApproved, model.NotifyPostRejected, model.NotifyLevelUp}
+	case "mention":
+		return []string{model.NotifyComment, model.NotifyCommentReply}
+	case "like":
+		return []string{model.NotifyLikeAggregated}
+	case "follow":
+		return []string{model.NotifyFollow}
+	default:
+		return []string{}
+	}
+}
+
+// sortNotifications 按 CreatedAt 降序排序
+func sortNotifications(items []model.Notification) {
+	sort.Slice(items, func(i, j int) bool {
+		return items[i].CreatedAt.After(items[j].CreatedAt)
+	})
+}
+
 // CountUnread 统计未读消息数
 func (s *NotificationService) CountUnread(userID uint) (int64, error) {
 	return s.repo.CountUnread(userID)
@@ -128,3 +257,25 @@ func (s *NotificationService) NotifyPostRejected(userID uint, postTitle, reason
 	}
 	_ = s.Create(userID, model.NotifyPostRejected, title, content, &postID, nil)
 }
+
+// NotifyFollow 关注通知（followerID 关注了 followeeID）
+func (s *NotificationService) NotifyFollow(followerID, followeeID uint) {
+	// 获取关注者用户名
+	followerName := s.getUsername(followerID)
+	if followerName == "" {
+		followerName = "一位用户"
+	}
+	title := "关注通知"
+	content := followerName + " 关注了你"
+	relID := followerID
+	_ = s.Create(followeeID, model.NotifyFollow, title, content, &relID, nil)
+}
+
+// getUsername 获取用户名（辅助方法）
+func (s *NotificationService) getUsername(userID uint) string {
+	name, err := s.repo.GetUsernameByID(userID)
+	if err != nil || name == "" {
+		return "一位用户"
+	}
+	return name
+}