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/controller/interfaces.go

@@ -103,3 +103,11 @@ type commentUseCase interface {
 	ListReplies(rootID uint) ([]model.Comment, error)
 	SearchUsers(keyword string) ([]model.UserSearchResult, error)
 }
+
+// reactionUseCase ReactionController 对 ReactionService 的最小依赖（ISP：4 个方法）
+type reactionUseCase interface {
+	ToggleLike(userID, postID uint) (bool, error)
+	ToggleDislike(userID, postID uint) (bool, error)
+	GetReaction(userID, postID uint) (service.ReactionType, error)
+	GetPostLikesCount(postID uint) (int, error)
+}

internal/controller/reaction_controller.go

@@ -0,0 +1,108 @@
+package controller
+
+import (
+	"net/http"
+	"strconv"
+
+	"metazone.cc/metalab/internal/common"
+	"metazone.cc/metalab/internal/service"
+
+	"github.com/gin-gonic/gin"
+)
+
+// ReactionController 赞/踩 API 控制器
+type ReactionController struct {
+	reactionSvc reactionUseCase
+}
+
+// NewReactionController 构造函数
+func NewReactionController(reactionSvc reactionUseCase) *ReactionController {
+	return &ReactionController{reactionSvc: reactionSvc}
+}
+
+// ToggleLike 切换点赞 POST /api/posts/:id/like
+func (rc *ReactionController) ToggleLike(c *gin.Context) {
+	uid, _, ok := common.GetGinUser(c)
+	if !ok {
+		common.Error(c, http.StatusUnauthorized, "请先登录")
+		return
+	}
+
+	postID, err := strconv.ParseUint(c.Param("id"), 10, 64)
+	if err != nil {
+		common.Error(c, http.StatusBadRequest, "无效的文章ID")
+		return
+	}
+
+	isLiked, err := rc.reactionSvc.ToggleLike(uid, uint(postID))
+	if err != nil {
+		common.Error(c, http.StatusInternalServerError, "操作失败")
+		return
+	}
+
+	// 获取最新点赞数
+	likesCount, _ := rc.reactionSvc.GetPostLikesCount(uint(postID))
+
+	common.Ok(c, gin.H{
+		"liked":       isLiked,
+		"likes_count": likesCount,
+	})
+}
+
+// ToggleDislike 切换踩 POST /api/posts/:id/dislike
+func (rc *ReactionController) ToggleDislike(c *gin.Context) {
+	uid, _, ok := common.GetGinUser(c)
+	if !ok {
+		common.Error(c, http.StatusUnauthorized, "请先登录")
+		return
+	}
+
+	postID, err := strconv.ParseUint(c.Param("id"), 10, 64)
+	if err != nil {
+		common.Error(c, http.StatusBadRequest, "无效的文章ID")
+		return
+	}
+
+	isDisliked, err := rc.reactionSvc.ToggleDislike(uid, uint(postID))
+	if err != nil {
+		common.Error(c, http.StatusInternalServerError, "操作失败")
+		return
+	}
+
+	common.Ok(c, gin.H{
+		"disliked": isDisliked,
+	})
+}
+
+// GetReaction 查询当前用户对文章的反应状态 GET /api/posts/:id/reaction
+func (rc *ReactionController) GetReaction(c *gin.Context) {
+	postID, err := strconv.ParseUint(c.Param("id"), 10, 64)
+	if err != nil {
+		common.Error(c, http.StatusBadRequest, "无效的文章ID")
+		return
+	}
+
+	// 未登录用户返回 none + 公开计数
+	uid, _, ok := common.GetGinUser(c)
+	if !ok {
+		likesCount, _ := rc.reactionSvc.GetPostLikesCount(uint(postID))
+		common.Ok(c, gin.H{
+			"reaction":    string(service.ReactionNone),
+			"likes_count": likesCount,
+		})
+		return
+	}
+
+	reaction, err := rc.reactionSvc.GetReaction(uid, uint(postID))
+	if err != nil {
+		common.Error(c, http.StatusInternalServerError, "查询失败")
+		return
+	}
+
+	likesCount, _ := rc.reactionSvc.GetPostLikesCount(uint(postID))
+
+	common.Ok(c, gin.H{
+		"reaction":    string(reaction),
+		"likes_count": likesCount,
+	})
+}