新功能(#74): 新增促销系统模型层

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

internal/model/subscribe_promo/subscribe_promo.go

@@ -0,0 +1,16 @@
+package subscribe_promo
+
+import "time"
+
+type SubscribePromo struct {
+	Id          int64     `gorm:"type:bigint unsigned;primaryKey"`
+	SubscribeId int64     `gorm:"type:bigint unsigned;not null;index:uk_subscribe_rule,unique,priority:1;comment:Subscribe Id"`
+	PromoRuleId int64     `gorm:"type:bigint unsigned;not null;index:uk_subscribe_rule,unique,priority:2;index:idx_promo_rule_id;comment:Promo Rule Id"`
+	PromoPrice  int64     `gorm:"type:bigint;not null;default:0;comment:Promo Price"`
+	CreatedAt   time.Time `gorm:"<-:create;comment:Create Time"`
+	UpdatedAt   time.Time `gorm:"comment:Update Time"`
+}
+
+func (SubscribePromo) TableName() string {
+	return "subscribe_promo"
+}