feat: 文章锁定/解锁时触发系统通知

- 新增 NotifyPostLocked/NotifyPostUnlocked 通知类型
- Lock/Unlock 方法执行后通过 notifier 发送通知给作者
- 锁定时通知含锁定理由，解锁时通知已解除锁定
- 新增类型归入稿件审核分类和 system tab

internal/service/notification_notify.go

@@ -47,7 +47,7 @@ func countUIDs(uids string) int {
 func categoryTypes(category string) []string {
 	switch category {
 	case "system":
-		return []string{model.NotifyAuditApproved, model.NotifyAuditRejected, model.NotifyPostApproved, model.NotifyPostRejected, model.NotifyLevelUp}
+		return []string{model.NotifyAuditApproved, model.NotifyAuditRejected, model.NotifyPostApproved, model.NotifyPostRejected, model.NotifyPostLocked, model.NotifyPostUnlocked, model.NotifyLevelUp}
 	case "mention":
 		return []string{model.NotifyComment, model.NotifyCommentReply}
 	case "like":
@@ -111,6 +111,24 @@ func (s *NotificationService) NotifyPostRejected(userID uint, postTitle, reason
 	_ = s.Create(userID, model.NotifyPostRejected, title, content, &postID, nil)
 }
 
+// NotifyPostLocked 稿件锁定通知
+func (s *NotificationService) NotifyPostLocked(userID uint, postTitle, reason string, postID uint) {
+	title := "稿件被锁定"
+	content := "你的稿件《" + postTitle + "》已被锁定"
+	if reason != "" {
+		content += "，理由：" + reason
+	}
+	_ = s.Create(userID, model.NotifyPostLocked, title, content, &postID, nil)
+}
+
+// NotifyPostUnlocked 稿件解除锁定通知
+func (s *NotificationService) NotifyPostUnlocked(userID uint, postTitle string, postID uint) {
+	_ = s.Create(userID, model.NotifyPostUnlocked,
+		"稿件被解除锁定",
+		"你的稿件《"+postTitle+"》已被解除锁定",
+		&postID, nil)
+}
+
 // NotifyFollow 关注通知（followerID 关注了 followeeID）
 func (s *NotificationService) NotifyFollow(followerID, followeeID uint) {
 	// 获取关注者用户名