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/coupons.gen.go

@@ -0,0 +1,64 @@
+// Code generated by go.ipao.vip/gen. DO NOT EDIT.
+// Code generated by go.ipao.vip/gen. DO NOT EDIT.
+// Code generated by go.ipao.vip/gen. DO NOT EDIT.
+
+package models
+
+import (
+	"context"
+	"time"
+
+	"go.ipao.vip/gen"
+)
+
+const TableNameCoupon = "coupons"
+
+// Coupon mapped from table <coupons>
+type Coupon struct {
+	ID             int64     `gorm:"column:id;type:bigint;primaryKey;autoIncrement:true" json:"id"`
+	TenantID       int64     `gorm:"column:tenant_id;type:bigint;not null" json:"tenant_id"`
+	Title          string    `gorm:"column:title;type:character varying(255);not null" json:"title"`
+	Description    string    `gorm:"column:description;type:text" json:"description"`
+	Type           string    `gorm:"column:type;type:character varying(32);not null" json:"type"`
+	Value          int64     `gorm:"column:value;type:bigint;not null" json:"value"`
+	MinOrderAmount int64     `gorm:"column:min_order_amount;type:bigint;not null" json:"min_order_amount"`
+	MaxDiscount    int64     `gorm:"column:max_discount;type:bigint" json:"max_discount"`
+	TotalQuantity  int32     `gorm:"column:total_quantity;type:integer;not null" json:"total_quantity"`
+	UsedQuantity   int32     `gorm:"column:used_quantity;type:integer;not null" json:"used_quantity"`
+	StartAt        time.Time `gorm:"column:start_at;type:timestamp with time zone" json:"start_at"`
+	EndAt          time.Time `gorm:"column:end_at;type:timestamp with time zone" json:"end_at"`
+	CreatedAt      time.Time `gorm:"column:created_at;type:timestamp with time zone;not null;default:now()" json:"created_at"`
+	UpdatedAt      time.Time `gorm:"column:updated_at;type:timestamp with time zone;not null;default:now()" json:"updated_at"`
+}
+
+// Quick operations without importing query package
+// Update applies changed fields to the database using the default DB.
+func (m *Coupon) Update(ctx context.Context) (gen.ResultInfo, error) {
+	return Q.Coupon.WithContext(ctx).Updates(m)
+}
+
+// Save upserts the model using the default DB.
+func (m *Coupon) Save(ctx context.Context) error { return Q.Coupon.WithContext(ctx).Save(m) }
+
+// Create inserts the model using the default DB.
+func (m *Coupon) Create(ctx context.Context) error { return Q.Coupon.WithContext(ctx).Create(m) }
+
+// Delete removes the row represented by the model using the default DB.
+func (m *Coupon) Delete(ctx context.Context) (gen.ResultInfo, error) {
+	return Q.Coupon.WithContext(ctx).Delete(m)
+}
+
+// ForceDelete permanently deletes the row (ignores soft delete) using the default DB.
+func (m *Coupon) ForceDelete(ctx context.Context) (gen.ResultInfo, error) {
+	return Q.Coupon.WithContext(ctx).Unscoped().Delete(m)
+}
+
+// Reload reloads the model from database by its primary key and overwrites current fields.
+func (m *Coupon) Reload(ctx context.Context) error {
+	fresh, err := Q.Coupon.WithContext(ctx).GetByID(m.ID)
+	if err != nil {
+		return err
+	}
+	*m = *fresh
+	return nil
+}