feat: 评论/帖子编辑历史与编辑标记，内容锁定

- 新增 smartDiff 差异计算与 EditHistoryModal 编辑历史弹窗，替换原 CommentEditHistoryModal
- 新增 PostEditedMark 编辑标记展示
- 新增内容锁定机制（content_lock）防止并发编辑冲突
- 审核与通知服务适配

backend/router/router.go

@@ -204,6 +204,9 @@ func Setup(cfg *config.Config) (*gin.Engine, error) {
 		api.PUT("/profile", h.UpdateProfile)
 		api.POST("/posts", middleware.StaffExempt(middleware.RateLimitMiddleware(limiter, service.RatePost)), h.CreatePost)
 		api.PUT("/posts/:id", h.UpdatePost)
+		api.GET("/posts/:id/history", h.PostEditHistory)
+		// 评论编辑历史（登录即可见；顶层路由：管理后台无 post_id 上下文）
+		api.GET("/comments/:cid/history", h.CommentEditHistory)
 		api.POST("/posts/:id/unlock", middleware.StaffExempt(middleware.RateLimitUserMiddleware(limiter, service.RateInteract)), h.UnlockPostContent)
 		api.POST("/posts/:id/poll/vote", middleware.StaffExempt(middleware.RateLimitUserMiddleware(limiter, service.RateInteract)), h.VotePoll)
 		api.POST("/posts/:id/poll/close", h.ClosePoll)
@@ -215,6 +218,7 @@ func Setup(cfg *config.Config) (*gin.Engine, error) {
 		api.DELETE("/posts/:id", h.DeletePost)
 		api.PUT("/posts/:id/pin", h.TogglePin)
 		api.PUT("/posts/:id/recommend", h.ToggleRecommend)
+		api.PUT("/posts/:id/lock", h.TogglePostLock)
 		api.POST("/posts/:id/like", h.ToggleLike)
 		api.POST("/posts/:id/comments", middleware.StaffExempt(middleware.RateLimitMiddleware(limiter, service.RateComment)), h.CreateComment)
 		api.PUT("/posts/:id/comments/:cid", middleware.StaffExempt(middleware.RateLimitMiddleware(limiter, service.RateComment)), h.UpdateComment)
@@ -293,7 +297,6 @@ func Setup(cfg *config.Config) (*gin.Engine, error) {
 		staffAPI.DELETE("/content/comments/:id", h.AdminSoftDeleteComment)
 		staffAPI.PUT("/content/comments/:id/restore", h.AdminRestoreComment)
 		staffAPI.DELETE("/content/comments/:id/purge", h.AdminPurgeComment)
-		staffAPI.GET("/content/comments/:id/history", h.AdminCommentHistory)
 
 		// 积分与类型帖概览（管理员及以上）
 		staffAPI.GET("/economy", authMW.RequirePerm(service.PermAnnouncements), h.AdminPointsStats)