feat(trade): connect WeChat refund API and callback flow

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

server/dukang-api/src/integrations/pay/pay.wechat.provider.ts

@@ -72,4 +72,40 @@ export class PayWechatProvider implements IPayProvider {
     });
     return { mode: 'jsapi', prepay };
   }
+
+  async refundOrder(
+    orderId: bigint,
+    outRefundNo: string,
+    reason?: string,
+  ) {
+    if (loadAppConfig().mockPay) {
+      return { mode: 'mock' as const, outRefundNo };
+    }
+    if (!this.wechat.isPayEnabled()) {
+      throw new Error('微信支付未配置：请关闭 MOCK_PAY 并配置 WX_MCH_ID 等商户参数');
+    }
+
+    const order = await this.prisma.order.findUnique({ where: { id: orderId } });
+    if (!order) throw new Error('订单不存在');
+
+    const amountFen = Math.round(Number(order.payAmount) * 100);
+    const notifyUrl = process.env.WX_REFUND_NOTIFY_URL ?? '';
+
+    this.logger.log(`create refund order=${order.orderNo} outRefundNo=${outRefundNo}`);
+    const result = await this.wechat.createDomesticRefund({
+      orderNo: order.orderNo,
+      transactionId: order.payExternalNo ?? undefined,
+      outRefundNo,
+      amountFen,
+      totalFen: amountFen,
+      reason,
+      notifyUrl,
+    });
+    return {
+      mode: 'wechat' as const,
+      outRefundNo: result.outRefundNo,
+      refundId: result.refundId,
+      status: result.status === 'SUCCESS' ? 'SUCCESS' as const : 'PROCESSING' as const,
+    };
+  }
 }