新功能(#74): 新增促销系统模型层

Co-authored-by: multica-agent <github@multica.ai>

internal/model/promo_usage/promo_usage.go

@@ -0,0 +1,17 @@
+package promo_usage
+
+import "time"
+
+type PromoUsage struct {
+	Id          int64     `gorm:"type:bigint unsigned;primaryKey"`
+	UserId      int64     `gorm:"type:bigint unsigned;not null;index:idx_user_rule,priority:1;comment:User Id"`
+	PromoRuleId int64     `gorm:"type:bigint unsigned;not null;index:idx_user_rule,priority:2;comment:Promo Rule Id"`
+	SubscribeId int64     `gorm:"type:bigint unsigned;not null;comment:Subscribe Id"`
+	OrderNo     string    `gorm:"type:varchar(255);not null;default:'';index:idx_order_no;comment:Order No"`
+	PromoPrice  int64     `gorm:"type:bigint;not null;default:0;comment:Promo Price"`
+	CreatedAt   time.Time `gorm:"<-:create;comment:Create Time"`
+}
+
+func (PromoUsage) TableName() string {
+	return "promo_usage"
+}