feat: add coupon support to orders and create user_coupons model

- Added CouponID field to Order model to track used coupons.
- Updated order query generation to include CouponID.
- Introduced UserCoupon model to manage user coupon associations.
- Implemented query methods for UserCoupon to facilitate CRUD operations.
- Updated query context and default query setup to include UserCoupon.

backend/database/models/orders.query.gen.go

@@ -43,6 +43,7 @@ func newOrder(db *gorm.DB, opts ...gen.DOOption) orderQuery {
 	_orderQuery.RefundReason = field.NewString(tableName, "refund_reason")
 	_orderQuery.CreatedAt = field.NewTime(tableName, "created_at")
 	_orderQuery.UpdatedAt = field.NewTime(tableName, "updated_at")
+	_orderQuery.CouponID = field.NewInt64(tableName, "coupon_id")
 
 	_orderQuery.fillFieldMap()
 
@@ -71,6 +72,7 @@ type orderQuery struct {
 	RefundReason         field.String
 	CreatedAt            field.Time
 	UpdatedAt            field.Time
+	CouponID             field.Int64 // 使用的优惠券ID (0表示未使用)
 
 	fieldMap map[string]field.Expr
 }
@@ -105,6 +107,7 @@ func (o *orderQuery) updateTableName(table string) *orderQuery {
 	o.RefundReason = field.NewString(table, "refund_reason")
 	o.CreatedAt = field.NewTime(table, "created_at")
 	o.UpdatedAt = field.NewTime(table, "updated_at")
+	o.CouponID = field.NewInt64(table, "coupon_id")
 
 	o.fillFieldMap()
 
@@ -135,7 +138,7 @@ func (o *orderQuery) GetFieldByName(fieldName string) (field.OrderExpr, bool) {
 }
 
 func (o *orderQuery) fillFieldMap() {
-	o.fieldMap = make(map[string]field.Expr, 18)
+	o.fieldMap = make(map[string]field.Expr, 19)
 	o.fieldMap["id"] = o.ID
 	o.fieldMap["tenant_id"] = o.TenantID
 	o.fieldMap["user_id"] = o.UserID
@@ -154,6 +157,7 @@ func (o *orderQuery) fillFieldMap() {
 	o.fieldMap["refund_reason"] = o.RefundReason
 	o.fieldMap["created_at"] = o.CreatedAt
 	o.fieldMap["updated_at"] = o.UpdatedAt
+	o.fieldMap["coupon_id"] = o.CouponID
 }
 
 func (o orderQuery) clone(db *gorm.DB) orderQuery {