feat(order): 添加零金额订单处理逻辑

- 在 getPaymentParams 方法中增加对订单金额的检查- 如果订单金额为 0 或空，则自动将订单状态设置为已支付
- 更新数据库中的订单信息
- 返回一个特殊的 PaymentParamsResponse，表示免费订单
-非零金额订单则按原有流程处理

src/main/java/com/ycwl/basic/service/pc/impl/OrderServiceImpl.java

@@ -843,10 +843,23 @@ public class OrderServiceImpl implements OrderService {
 
     @Override
     public ApiResponse<PaymentParamsResponse> getPaymentParams(Long orderId, Long userId, PaymentParamsRequest request) {
+        OrderEntity order = orderMapper.get(orderId);
+        
+        // 检查订单金额是否为0
+        if (order.getPayPrice() == null || order.getPayPrice().compareTo(BigDecimal.ZERO) == 0) {
+            // 零金额订单：设置needPay为false，直接标记为已支付
+            order.setStatus(1); // 1表示已支付
+            order.setPayAt(new Date());
+            orderMapper.updateOrder(order);
+            
+            // 返回免费订单响应
+            return ApiResponse.success(PaymentParamsResponse.free(orderId, orderId.toString()));
+        }
+        
+        // 非零金额订单：按原流程处理
         PaymentParamsResponse response = new PaymentParamsResponse();
         response.setOrderId(orderId);
         response.setOrderNo(orderId.toString());
-        OrderEntity order = orderMapper.get(orderId);
         response.setNeedPay(true);
         List<OrderItemEntity> orderItems = orderMapper.getOrderItems(orderId);
         try {