feat(erp): 添加单箱金额字段并移除清关总价字段

- 在销售产品、出货产品等多个结构体中添加 BoxAmount（单箱金额）字段
- 移除出货产品结构体中的 ClearanceAmount（清关总价）字段
- 涉及 sale/product、shipment/saleProduct、shipment/modify/saleProduct、shipment/mixed/product 等模块

erp/shipment/mixed/product.go

@@ -38,6 +38,7 @@ type ProductItem struct {
 	FactoryName                 string           `json:"factoryName"`
 	SalePrice                   decimal.Decimal  `json:"salePrice"`
 	SaleAmount                  decimal.Decimal  `json:"saleAmount"`
+	BoxAmount                   decimal.Decimal  `json:"boxAmount"`
 	CustomsPrice                decimal.Decimal  `json:"customsPrice"`
 	CustomsAmount               decimal.Decimal  `json:"customsAmount"`
 	OuterLength                 *decimal.Decimal `json:"outerLength"`