task: 完成支付宝共享基础（迁移/WechatConfig/PaymentStore/pkg/alipay）

internal/store/postgres/payment_store.go

@@ -150,3 +150,18 @@ func (s *PaymentStore) GetByOrderIDAndStatus(ctx context.Context, orderID uint,
 	}
 	return &payment, nil
 }
+
+// FindLatestPendingByOrderAndMethod 按业务单、支付方式查找最新一条待支付记录
+// 用于支付宝支付单复用：同一业务单同一支付方式只允许一个有效 pending 支付单
+func (s *PaymentStore) FindLatestPendingByOrderAndMethod(ctx context.Context, orderID uint, orderType string, paymentMethod string) (*model.Payment, error) {
+	var payment model.Payment
+	err := s.db.WithContext(ctx).
+		Where("order_id = ? AND order_type = ? AND payment_method = ? AND status = ?",
+			orderID, orderType, paymentMethod, model.PaymentRecordStatusPending).
+		Order("created_at DESC").
+		First(&payment).Error
+	if err != nil {
+		return nil, err
+	}
+	return &payment, nil
+}