优化交易创建流程，客户管理新增折扣与来源字段及功能

web/models/product_discount.go

@@ -13,7 +13,7 @@ type ProductDiscount struct {
 	Discount int32  `json:"discount" gorm:"column:discount"` // 产品折扣
 }
 
-func (pd ProductDiscount) Decimal() decimal.Decimal {
+func (pd ProductDiscount) Rate() decimal.Decimal {
 	return decimal.NewFromInt32(pd.Discount).
 		Div(decimal.NewFromInt32(100))
 }