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/repository/reaction_repo.go

@@ -0,0 +1,77 @@
+package repository
+
+import (
+	"metazone.cc/metalab/internal/model"
+	"metazone.cc/metalab/internal/service"
+
+	"gorm.io/gorm"
+)
+
+// ReactionRepo 赞/踩数据访问
+type ReactionRepo struct {
+	db *gorm.DB
+}
+
+// NewReactionRepo 构造函数
+func NewReactionRepo(db *gorm.DB) *ReactionRepo {
+	return &ReactionRepo{db: db}
+}
+
+// WithTx 基于给定事务连接创建新的 ReactionRepo
+func (r *ReactionRepo) WithTx(tx *gorm.DB) service.ReactionStore {
+	return &ReactionRepo{db: tx}
+}
+
+// FindLike 查找点赞记录
+func (r *ReactionRepo) FindLike(userID, postID uint) (*model.PostLike, error) {
+	var like model.PostLike
+	err := r.db.Where("user_id = ? AND post_id = ?", userID, postID).First(&like).Error
+	if err != nil {
+		return nil, err
+	}
+	return &like, nil
+}
+
+// CreateLike 创建点赞记录
+func (r *ReactionRepo) CreateLike(like *model.PostLike) error {
+	return r.db.Create(like).Error
+}
+
+// DeleteLike 删除点赞记录
+func (r *ReactionRepo) DeleteLike(userID, postID uint) error {
+	return r.db.Where("user_id = ? AND post_id = ?", userID, postID).Delete(&model.PostLike{}).Error
+}
+
+// FindDislike 查找踩记录
+func (r *ReactionRepo) FindDislike(userID, postID uint) (*model.PostDislike, error) {
+	var dislike model.PostDislike
+	err := r.db.Where("user_id = ? AND post_id = ?", userID, postID).First(&dislike).Error
+	if err != nil {
+		return nil, err
+	}
+	return &dislike, nil
+}
+
+// CreateDislike 创建踩记录
+func (r *ReactionRepo) CreateDislike(dislike *model.PostDislike) error {
+	return r.db.Create(dislike).Error
+}
+
+// DeleteDislike 删除踩记录
+func (r *ReactionRepo) DeleteDislike(userID, postID uint) error {
+	return r.db.Where("user_id = ? AND post_id = ?", userID, postID).Delete(&model.PostDislike{}).Error
+}
+
+// IncrPostLikes 原子增加文章点赞数
+func (r *ReactionRepo) IncrPostLikes(postID uint, delta int) error {
+	return r.db.Model(&model.Post{}).
+		Where("id = ?", postID).
+		UpdateColumn("likes_count", gorm.Expr("likes_count + ?", delta)).Error
+}
+
+// IncrPostDislikes 原子增加文章踩数
+func (r *ReactionRepo) IncrPostDislikes(postID uint, delta int) error {
+	return r.db.Model(&model.Post{}).
+		Where("id = ?", postID).
+		UpdateColumn("dislikes_count", gorm.Expr("dislikes_count + ?", delta)).Error
+}