feat: 实现赞/踩系统（P2）

- 新增 PostLike/PostDislike 模型，复合主键 (user_id, post_id)
- Post 表新增 LikesCount/DislikesCount 冗余计数器
- Repository 层：reaction_repo.go，含 WithTx 事务支持
- Service 层：reaction_service.go，赞踩互斥逻辑（6 态切换），事务包裹
- Controller 层：reaction_controller.go，3 个 API（ToggleLike/ToggleDislike/GetReaction）
- 接口定义：controller/interfaces.go 新增 reactionUseCase，service/repository.go 新增 ReactionStore
- 路由注册 + 依赖注入 + AutoMigrate
- 前端：文章详情页赞踩按钮 + 状态查询 + 401 跳转登录
- 样式：posts.css 新增赞踩按钮样式

internal/service/reaction_service.go

@@ -0,0 +1,155 @@
+package service
+
+import (
+	"fmt"
+
+	"metazone.cc/metalab/internal/common"
+	"metazone.cc/metalab/internal/model"
+
+	"gorm.io/gorm"
+)
+
+// ReactionType 反应类型
+type ReactionType string
+
+const (
+	ReactionNone    ReactionType = "none"
+	ReactionLiked   ReactionType = "liked"
+	ReactionDisliked ReactionType = "disliked"
+)
+
+// 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}
+}
+
+// ToggleLike 切换点赞（含踩互斥逻辑）
+// 返回：当前是否已点赞
+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)
+
+		// 查当前状态
+		_, likeErr := txRepo.FindLike(userID, postID)
+		hasLike := likeErr == nil
+
+		_, dislikeErr := txRepo.FindDislike(userID, postID)
+		hasDislike := dislikeErr == nil
+
+		if hasLike {
+			// 已赞 → 取消赞
+			if err := txRepo.DeleteLike(userID, postID); err != nil {
+				return fmt.Errorf("取消点赞失败: %w", err)
+			}
+			if err := txRepo.IncrPostLikes(postID, -1); err != nil {
+				return fmt.Errorf("更新点赞计数失败: %w", err)
+			}
+			isLiked = false
+		} else {
+			// 无赞 → 加赞（若已有踩，先移除踩）
+			if hasDislike {
+				if err := txRepo.DeleteDislike(userID, postID); err != nil {
+					return fmt.Errorf("移除踩记录失败: %w", err)
+				}
+				if err := txRepo.IncrPostDislikes(postID, -1); err != nil {
+					return fmt.Errorf("更新踩计数失败: %w", err)
+				}
+			}
+
+			if err := txRepo.CreateLike(&model.PostLike{UserID: userID, PostID: postID}); err != nil {
+				return fmt.Errorf("创建点赞记录失败: %w", err)
+			}
+			if err := txRepo.IncrPostLikes(postID, 1); err != nil {
+				return fmt.Errorf("更新点赞计数失败: %w", err)
+			}
+			isLiked = true
+		}
+		return nil
+	})
+
+	return isLiked, err
+}
+
+// ToggleDislike 切换踩（含赞互斥逻辑）
+// 返回：当前是否已踩
+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)
+
+		// 查当前状态
+		_, likeErr := txRepo.FindLike(userID, postID)
+		hasLike := likeErr == nil
+
+		_, dislikeErr := txRepo.FindDislike(userID, postID)
+		hasDislike := dislikeErr == nil
+
+		if hasDislike {
+			// 已踩 → 取消踩
+			if err := txRepo.DeleteDislike(userID, postID); err != nil {
+				return fmt.Errorf("取消踩失败: %w", err)
+			}
+			if err := txRepo.IncrPostDislikes(postID, -1); err != nil {
+				return fmt.Errorf("更新踩计数失败: %w", err)
+			}
+			isDisliked = false
+		} else {
+			// 无踩 → 加踩（若已有赞，先移除赞）
+			if hasLike {
+				if err := txRepo.DeleteLike(userID, postID); err != nil {
+					return fmt.Errorf("移除点赞记录失败: %w", err)
+				}
+				if err := txRepo.IncrPostLikes(postID, -1); err != nil {
+					return fmt.Errorf("更新点赞计数失败: %w", err)
+				}
+			}
+
+			if err := txRepo.CreateDislike(&model.PostDislike{UserID: userID, PostID: postID}); err != nil {
+				return fmt.Errorf("创建踩记录失败: %w", err)
+			}
+			if err := txRepo.IncrPostDislikes(postID, 1); err != nil {
+				return fmt.Errorf("更新踩计数失败: %w", err)
+			}
+			isDisliked = true
+		}
+		return nil
+	})
+
+	return isDisliked, err
+}
+
+// GetReaction 查询用户对文章的反应状态
+func (s *ReactionService) GetReaction(userID, postID uint) (ReactionType, error) {
+	_, likeErr := s.repo.FindLike(userID, postID)
+	if likeErr == nil {
+		return ReactionLiked, nil
+	}
+
+	_, dislikeErr := s.repo.FindDislike(userID, postID)
+	if dislikeErr == nil {
+		return ReactionDisliked, nil
+	}
+
+	return ReactionNone, nil
+}
+
+// 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)
+	}
+	return post.LikesCount, nil
+}