feat(moderation): add manual content review system with three-tier AI moderation

Add admin comment moderation endpoints (single and batch) and introduce a three-tier moderation system (pass/review/block) for content flagged by AI. Content with unclear violations is now held for manual review instead of being auto-rejected. Deleted the legacy audit_service.go in favor of the unified hook-based moderation system.

internal/repository/comment_repo.go

@@ -13,7 +13,7 @@ type CommentRepository interface {
 	Create(comment *model.Comment) error
 	GetByID(id string) (*model.Comment, error)
 	Update(comment *model.Comment) error
-	UpdateModerationStatus(commentID string, status model.CommentStatus) error
+	UpdateModerationStatus(commentID string, status model.CommentStatus, rejectReason string, reviewedBy string) error
 	Delete(id string) error
 	ApplyPublishedStats(comment *model.Comment) error
 	GetByPostID(postID string, page, pageSize int) ([]*model.Comment, int64, error)
@@ -63,11 +63,17 @@ func (r *commentRepository) Update(comment *model.Comment) error {
 }
 
 // UpdateModerationStatus 更新评论审核状态
-func (r *commentRepository) UpdateModerationStatus(commentID string, status model.CommentStatus) error {
-	// 审核状态更新属于管理操作，不应影响评论内容更新时间（updated_at）
+func (r *commentRepository) UpdateModerationStatus(commentID string, status model.CommentStatus, rejectReason string, reviewedBy string) error {
+	updates := map[string]any{
+		"status":        status,
+		"reviewed_at":   gorm.Expr("CURRENT_TIMESTAMP"),
+		"reviewed_by":   reviewedBy,
+		"reject_reason": rejectReason,
+		"updated_at":    gorm.Expr("updated_at"),
+	}
 	return r.db.Model(&model.Comment{}).
 		Where("id = ?", commentID).
-		UpdateColumn("status", status).Error
+		UpdateColumns(updates).Error
 }
 
 // Delete 删除评论（软删除，同时清理关联数据）