fix: 修复C端订单差价佣金计算错误及自动购包订单系列ID缺失问题

- C端普通订单（createPackageOrder）创建时未设置 SellerCostPrice，
  导致底层店铺得到整个零售价作为差价佣金，上级代理链无法获得任何佣金。
  修复：在 createPackageOrder 中查询卖家成本价并写入订单字段。

- purchase_validation 新增 GetCostPrice 方法，供 C 端订单查询代理渠道成本价。

- auto_purchase 自动购包订单未设置 SeriesID 和 SellerCostPrice，
  导致差价佣金计算被整体跳过。修复：在 ProcessTask 中从卡/设备获取
  SeriesID，从套餐分配记录获取 SellerCostPrice，传入 buildOrderAndItems。

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/service/client_order/service.go

@@ -284,7 +284,19 @@ func (s *Service) createPackageOrder(
 	redisKey string,
 	created *bool,
 ) (*dto.ClientCreateOrderResponse, error) {
-	order, err := s.buildPendingOrder(customerID, validationResult)
+	// 查询卖家成本价，用于差价佣金链式计算的起点
+	// 平台直销（sellerShopID == 0）时成本价为 0，CalculateCostDiffCommission 会直接跳过
+	var sellerCostPrice int64
+	sellerShopID := resolveSellerShopID(validationResult)
+	if sellerShopID > 0 && len(validationResult.Packages) > 0 {
+		costPrice, err := s.purchaseValidationService.GetCostPrice(ctx, validationResult.Packages[0], sellerShopID)
+		if err != nil {
+			return nil, errors.Wrap(errors.CodeInternalError, err, "查询卖家成本价失败")
+		}
+		sellerCostPrice = costPrice
+	}
+
+	order, err := s.buildPendingOrder(customerID, validationResult, sellerCostPrice)
 	if err != nil {
 		return nil, err
 	}
@@ -389,7 +401,7 @@ func (s *Service) createForceRechargeOrder(
 	}, nil
 }
 
-func (s *Service) buildPendingOrder(customerID uint, result *purchase_validation.PurchaseValidationResult) (*model.Order, error) {
+func (s *Service) buildPendingOrder(customerID uint, result *purchase_validation.PurchaseValidationResult, sellerCostPrice int64) (*model.Order, error) {
 	orderType := resolveOrderType(result)
 	if orderType == "" {
 		return nil, errors.New(errors.CodeInvalidParam)
@@ -413,6 +425,7 @@ func (s *Service) buildPendingOrder(customerID uint, result *purchase_validation
 		Source:                  constants.OrderSourceClient,
 		Generation:              resolveGeneration(result),
 		ExpiresAt:               &expiresAt,
+		SellerCostPrice:         sellerCostPrice,
 	}
 
 	if result.Card != nil {