退款审核功能：待交接取消不再自动退款，改为客服审核后原路退回

- 租客在待交接状态取消订单不再自动退款，改为 refund_status=pending_review
- 新增退款审核页面 /admin/orders/refund-review，客服可逐个审核
- 新增 POST /refund/approve 通过退款、POST /refund/reject 驳回退款
- 新增 GET /orders/refund-pending 查询待审核退款订单列表
- 优化状态标签表述：已取消→租客已取消、已关闭→客服已关闭、异常→客服介入
- 新增 refund_status: pending_review 及其前端标签「待客服审核退款」
- AdminOrderDetailView 退款状态改用统一 refundStatusLabel

backend/internal/modules/order/constants.go

@@ -39,8 +39,9 @@ const (
 	checkoutStatusAccepted  = "accepted"
 	checkoutStatusDisputed  = "disputed"
 
-	refundStatusPending  = "pending"
-	refundStatusRefunded = "refunded"
+	refundStatusPending       = "pending"
+	refundStatusPendingReview = "pending_review"
+	refundStatusRefunded      = "refunded"
 
 	listingReviewStatusApproved = "approved"