fix: 支付回调补写 actual_paid_amount 字段，从支付平台回调中提取实付金额

- HandlePaymentCallback 新增 actualPaidAmount int64 参数，Updates 写入 actual_paid_amount
- 微信 V2 回调从 TotalFee 字符串解析分值；V3 直接使用 TotalAmount
- 支付宝回调优先取 buyer_pay_amount（实付），回退 total_amount，元转分使用 math.Round
- 富友回调从 OrderAmt 字符串解析分值
- dispatchWechatCallback 同步增加 paidAmount 参数透传

internal/service/order/service.go

@@ -1410,7 +1410,7 @@ func (s *Service) WalletPay(ctx context.Context, orderID uint, buyerType string,
 	return nil
 }
 
-func (s *Service) HandlePaymentCallback(ctx context.Context, orderNo string, paymentMethod string) error {
+func (s *Service) HandlePaymentCallback(ctx context.Context, orderNo string, paymentMethod string, actualPaidAmount int64) error {
 	order, err := s.orderStore.GetByOrderNo(ctx, orderNo)
 	if err != nil {
 		if err == gorm.ErrRecordNotFound {
@@ -1424,10 +1424,11 @@ func (s *Service) HandlePaymentCallback(ctx context.Context, orderNo string, pay
 		result := tx.Model(&model.Order{}).
 			Where("id = ? AND payment_status = ?", order.ID, model.PaymentStatusPending).
 			Updates(map[string]any{
-				"payment_status": model.PaymentStatusPaid,
-				"payment_method": paymentMethod,
-				"paid_at":        now,
-				"expires_at":     nil, // 支付成功，清除过期时间
+				"payment_status":     model.PaymentStatusPaid,
+				"payment_method":     paymentMethod,
+				"paid_at":            now,
+				"expires_at":         nil, // 支付成功，清除过期时间
+				"actual_paid_amount": actualPaidAmount,
 			})
 		if result.Error != nil {
 			return errors.Wrap(errors.CodeDatabaseError, result.Error, "更新订单支付状态失败")