feat(moderation): 帖评删除占位感知与硬删清场

管理删帖须填类型与理由并展示专用页；评论软删占位、版主可硬删不占楼。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/service/admin_content.go

@@ -303,16 +303,38 @@ func (s *ModerationService) loadCommentUnscoped(actor *Actor, id uint) (*model.C
 	return &cm, post.BoardID, nil
 }
 
-// SoftDeletePost 软删帖子（未删除时）
-func (s *ModerationService) SoftDeletePost(actor *Actor, id uint) error {
+// SoftDeletePost 软删帖子（未删除时）；须填写删除类型与理由，并通知作者
+func (s *ModerationService) SoftDeletePost(actor *Actor, id uint, deleteType, deleteReason string) (authorID uint, err error) {
 	post, err := s.loadPostUnscoped(actor, id)
 	if err != nil {
-		return err
+		return 0, err
 	}
 	if post.DeletedAt.Valid {
-		return errors.New("帖子已在回收站")
+		return 0, errors.New("帖子已在回收站")
 	}
-	return s.db.Delete(post).Error
+	deleteType = strings.TrimSpace(deleteType)
+	deleteReason = strings.TrimSpace(deleteReason)
+	if !model.ValidPostDeleteType(deleteType) {
+		return 0, errors.New("无效的删除类型")
+	}
+	if deleteReason == "" {
+		return 0, errors.New("请填写删除理由")
+	}
+	if len([]rune(deleteReason)) > 200 {
+		return 0, errors.New("删除理由不能超过 200 字")
+	}
+	updates := map[string]interface{}{
+		"delete_type":   deleteType,
+		"delete_reason": deleteReason,
+		"deleted_by":    actor.ID,
+	}
+	if err := s.db.Model(post).Updates(updates).Error; err != nil {
+		return 0, err
+	}
+	if err := s.db.Delete(post).Error; err != nil {
+		return 0, err
+	}
+	return post.UserID, nil
 }
 
 // RestorePost 从回收站恢复帖子