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/service/setting.go

@@ -59,6 +59,12 @@ const (
 	// SettingKeyAnalyticsRetentionDays 访问明细保留天数；缺行=90
 	SettingKeyAnalyticsRetentionDays = "analytics_retention_days"
 
+	// 内容锁定与旧帖回复（全部缺行=0 关闭）
+	SettingKeyPostEditLockHours    = "post_edit_lock_hours"    // 帖子可编辑时长；0=不锁定
+	SettingKeyCommentEditLockHours = "comment_edit_lock_hours" // 评论可编辑时长；0=不锁定
+	SettingKeyNecroReplyAfterHours = "necro_reply_after_hours" // 超过该时长回复视为旧帖回复；0=关闭
+	SettingKeyNecroReplyPenalty    = "necro_reply_penalty"     // 旧帖回复扣除积分；0=仅提醒不扣分
+
 	// 积分增长规则（正整数奖励；0=关闭/不限，缺行=默认值）
 	SettingKeyPointsCheckinBase     = "points_checkin_base"     // 签到基础分；缺行=5
 	SettingKeyPointsStreakEveryDays = "points_streak_every_days" // 每满 N 天连续签到触发加成；0=关闭；缺行=7
@@ -100,6 +106,9 @@ const (
 	MinAnalyticsRetentionDays     = 7
 	MaxAnalyticsRetentionDays     = 365
 
+	// MaxContentLockHours 内容锁定/旧帖阈值小时数上限（一年）
+	MaxContentLockHours = 8760
+
 	DefaultPointsCheckinBase     = 5
 	DefaultPointsStreakEveryDays = 7
 	MaxPointsRule                = 100 // 各积分规则值/上限的统一上界
@@ -150,6 +159,12 @@ type PublicSiteSettings struct {
 	AttachmentMaxMB      int          `json:"attachment_max_mb"`
 	AttachmentMaxCount   int          `json:"attachment_max_count"`
 	ImageMaxMB           int          `json:"image_max_mb"`
+
+	// 内容锁定与旧帖回复（0=关闭；公开保持规则透明）
+	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"`
 	BgSiteURL            string       `json:"bg_site_url"`
 	BgSiteMode           string       `json:"bg_site_mode"`
 	BgAdminURL           string       `json:"bg_admin_url"`
@@ -438,6 +453,27 @@ func (s *SettingService) Public() (PublicSiteSettings, error) {
 	}
 	out.ImageMaxMB = imgMB
 
+	postLock, err := s.PostEditLockHours()
+	if err != nil {
+		return out, err
+	}
+	out.PostEditLockHours = postLock
+	commentLock, err := s.CommentEditLockHours()
+	if err != nil {
+		return out, err
+	}
+	out.CommentEditLockHours = commentLock
+	necroAfter, err := s.NecroReplyAfterHours()
+	if err != nil {
+		return out, err
+	}
+	out.NecroReplyAfterHours = necroAfter
+	necroPenalty, err := s.NecroReplyPenalty()
+	if err != nil {
+		return out, err
+	}
+	out.NecroReplyPenalty = necroPenalty
+
 	siteURL, err := s.BgSiteURL()
 	if err != nil {
 		return out, err
@@ -941,6 +977,91 @@ func (s *SettingService) ImageMaxBytes() (int64, error) {
 	return int64(mb) << 20, nil
 }
 
+// getLockHours 读取小时数配置（缺行/非法=0 关闭，超上限钳制）
+func (s *SettingService) getLockHours(key string) (int, error) {
+	v, found, err := s.getValue(key)
+	if err != nil {
+		return 0, err
+	}
+	if !found {
+		return 0, nil
+	}
+	n, convErr := strconv.Atoi(strings.TrimSpace(v))
+	if convErr != nil || n < 0 {
+		return 0, nil
+	}
+	if n > MaxContentLockHours {
+		return MaxContentLockHours, nil
+	}
+	return n, nil
+}
+
+func (s *SettingService) setLockHours(key string, hours int) error {
+	if hours < 0 || hours > MaxContentLockHours {
+		return ErrInvalidSiteSetting
+	}
+	if hours == 0 {
+		return s.deleteKey(key)
+	}
+	return s.putValue(key, strconv.Itoa(hours))
+}
+
+// PostEditLockHours 帖子可编辑时长（小时）。缺行=0（不锁定）。
+func (s *SettingService) PostEditLockHours() (int, error) {
+	return s.getLockHours(SettingKeyPostEditLockHours)
+}
+
+func (s *SettingService) SetPostEditLockHours(hours int) error {
+	return s.setLockHours(SettingKeyPostEditLockHours, hours)
+}
+
+// CommentEditLockHours 评论可编辑时长（小时）。缺行=0（不锁定）。
+func (s *SettingService) CommentEditLockHours() (int, error) {
+	return s.getLockHours(SettingKeyCommentEditLockHours)
+}
+
+func (s *SettingService) SetCommentEditLockHours(hours int) error {
+	return s.setLockHours(SettingKeyCommentEditLockHours, hours)
+}
+
+// NecroReplyAfterHours 旧帖回复阈值（小时）。缺行=0（关闭）。
+func (s *SettingService) NecroReplyAfterHours() (int, error) {
+	return s.getLockHours(SettingKeyNecroReplyAfterHours)
+}
+
+func (s *SettingService) SetNecroReplyAfterHours(hours int) error {
+	return s.setLockHours(SettingKeyNecroReplyAfterHours, hours)
+}
+
+// NecroReplyPenalty 旧帖回复扣分。缺行=0（仅提醒不扣分）。
+func (s *SettingService) NecroReplyPenalty() (int, error) {
+	v, found, err := s.getValue(SettingKeyNecroReplyPenalty)
+	if err != nil {
+		return 0, err
+	}
+	if !found {
+		return 0, nil
+	}
+	n, convErr := strconv.Atoi(strings.TrimSpace(v))
+	if convErr != nil || n < 0 {
+		return 0, nil
+	}
+	if n > MaxPointsRule {
+		return MaxPointsRule, nil
+	}
+	return n, nil
+}
+
+func (s *SettingService) SetNecroReplyPenalty(n int) error {
+	if n < 0 || n > MaxPointsRule {
+		return ErrInvalidSiteSetting
+	}
+	if n == 0 {
+		return s.deleteKey(SettingKeyNecroReplyPenalty)
+	}
+	return s.putValue(SettingKeyNecroReplyPenalty, strconv.Itoa(n))
+}
+
 // AnalyticsEnabled 访问统计采集开关。缺行视为开启。
 func (s *SettingService) AnalyticsEnabled() (bool, error) {
 	v, found, err := s.getValue(SettingKeyAnalyticsEnabled)