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/handler/setting.go

@@ -68,6 +68,11 @@ type updateSettingsRequest struct {
 	PointsReplyDailyCap   *int `json:"points_reply_daily_cap"`
 	PointsRecommendReward *int `json:"points_recommend_reward"`
 
+	PostEditLockHours    *int `json:"post_edit_lock_hours"`
+	CommentEditLockHours *int `json:"comment_edit_lock_hours"`
+	NecroReplyAfterHours *int `json:"necro_reply_after_hours"`
+	NecroReplyPenalty    *int `json:"necro_reply_penalty"`
+
 	Levels *[]model.LevelDef `json:"levels"`
 	LevelsFx *bool           `json:"levels_fx"`
 }
@@ -120,6 +125,11 @@ func settingsPayload(saved service.PublicSiteSettings) gin.H {
 		"points_reply_daily_cap":   saved.PointsReplyDailyCap,
 		"points_recommend_reward":  saved.PointsRecommendReward,
 
+		"post_edit_lock_hours":     saved.PostEditLockHours,
+		"comment_edit_lock_hours":  saved.CommentEditLockHours,
+		"necro_reply_after_hours":  saved.NecroReplyAfterHours,
+		"necro_reply_penalty":      saved.NecroReplyPenalty,
+
 		"levels": saved.Levels,
 		"levels_fx": saved.LevelsFx,
 	}
@@ -142,7 +152,9 @@ func (req *updateSettingsRequest) hasAny() bool {
 		req.PointsCheckinBase != nil || req.PointsStreakEveryDays != nil || req.PointsStreakBonus != nil ||
 		req.PointsPostReward != nil || req.PointsPostDailyCap != nil ||
 		req.PointsReplyReward != nil || req.PointsReplyDailyCap != nil ||
-		req.PointsRecommendReward != nil || req.Levels != nil || req.LevelsFx != nil
+		req.PointsRecommendReward != nil || req.Levels != nil || req.LevelsFx != nil ||
+		req.PostEditLockHours != nil || req.CommentEditLockHours != nil ||
+		req.NecroReplyAfterHours != nil || req.NecroReplyPenalty != nil
 }
 
 // AdminGetSettings 超管读取站点设置（与公开 payload 字段一致）
@@ -247,6 +259,29 @@ func (h *Handlers) UpdateSettings(c *gin.Context) {
 			return
 		}
 	}
+	lockRules := []struct {
+		req  *int
+		set  func(int) error
+		hint string
+	}{
+		{req.PostEditLockHours, h.Setting.SetPostEditLockHours, "帖子可编辑时长须为 0–8760 小时"},
+		{req.CommentEditLockHours, h.Setting.SetCommentEditLockHours, "评论可编辑时长须为 0–8760 小时"},
+		{req.NecroReplyAfterHours, h.Setting.SetNecroReplyAfterHours, "旧帖回复阈值须为 0–8760 小时"},
+		{req.NecroReplyPenalty, h.Setting.SetNecroReplyPenalty, "旧帖回复扣分须为 0–100"},
+	}
+	for _, r := range lockRules {
+		if r.req == nil {
+			continue
+		}
+		if err := r.set(*r.req); err != nil {
+			if errors.Is(err, service.ErrInvalidSiteSetting) {
+				c.JSON(http.StatusBadRequest, gin.H{"error": r.hint})
+				return
+			}
+			c.JSON(http.StatusInternalServerError, gin.H{"error": "保存站点设置失败"})
+			return
+		}
+	}
 	pointsRules := []struct {
 		req  *int
 		set  func(int) error