feat: 实现注册优惠码功能

- 支持创建/编辑/删除优惠码，设置赠送金额和使用限制
  - 注册页面实时验证优惠码并显示赠送金额
  - 支持 URL 参数自动填充 (?promo=CODE)
  - 添加优惠码验证接口速率限制
  - 使用数据库行锁防止并发超限
  - 新增后台优惠码管理页面，支持复制注册链接

backend/ent/promocodeusage_delete.go

@@ -0,0 +1,88 @@
+// Code generated by ent, DO NOT EDIT.
+
+package ent
+
+import (
+	"context"
+
+	"entgo.io/ent/dialect/sql"
+	"entgo.io/ent/dialect/sql/sqlgraph"
+	"entgo.io/ent/schema/field"
+	"github.com/Wei-Shaw/sub2api/ent/predicate"
+	"github.com/Wei-Shaw/sub2api/ent/promocodeusage"
+)
+
+// PromoCodeUsageDelete is the builder for deleting a PromoCodeUsage entity.
+type PromoCodeUsageDelete struct {
+	config
+	hooks    []Hook
+	mutation *PromoCodeUsageMutation
+}
+
+// Where appends a list predicates to the PromoCodeUsageDelete builder.
+func (_d *PromoCodeUsageDelete) Where(ps ...predicate.PromoCodeUsage) *PromoCodeUsageDelete {
+	_d.mutation.Where(ps...)
+	return _d
+}
+
+// Exec executes the deletion query and returns how many vertices were deleted.
+func (_d *PromoCodeUsageDelete) Exec(ctx context.Context) (int, error) {
+	return withHooks(ctx, _d.sqlExec, _d.mutation, _d.hooks)
+}
+
+// ExecX is like Exec, but panics if an error occurs.
+func (_d *PromoCodeUsageDelete) ExecX(ctx context.Context) int {
+	n, err := _d.Exec(ctx)
+	if err != nil {
+		panic(err)
+	}
+	return n
+}
+
+func (_d *PromoCodeUsageDelete) sqlExec(ctx context.Context) (int, error) {
+	_spec := sqlgraph.NewDeleteSpec(promocodeusage.Table, sqlgraph.NewFieldSpec(promocodeusage.FieldID, field.TypeInt64))
+	if ps := _d.mutation.predicates; len(ps) > 0 {
+		_spec.Predicate = func(selector *sql.Selector) {
+			for i := range ps {
+				ps[i](selector)
+			}
+		}
+	}
+	affected, err := sqlgraph.DeleteNodes(ctx, _d.driver, _spec)
+	if err != nil && sqlgraph.IsConstraintError(err) {
+		err = &ConstraintError{msg: err.Error(), wrap: err}
+	}
+	_d.mutation.done = true
+	return affected, err
+}
+
+// PromoCodeUsageDeleteOne is the builder for deleting a single PromoCodeUsage entity.
+type PromoCodeUsageDeleteOne struct {
+	_d *PromoCodeUsageDelete
+}
+
+// Where appends a list predicates to the PromoCodeUsageDelete builder.
+func (_d *PromoCodeUsageDeleteOne) Where(ps ...predicate.PromoCodeUsage) *PromoCodeUsageDeleteOne {
+	_d._d.mutation.Where(ps...)
+	return _d
+}
+
+// Exec executes the deletion query.
+func (_d *PromoCodeUsageDeleteOne) Exec(ctx context.Context) error {
+	n, err := _d._d.Exec(ctx)
+	switch {
+	case err != nil:
+		return err
+	case n == 0:
+		return &NotFoundError{promocodeusage.Label}
+	default:
+		return nil
+	}
+}
+
+// ExecX is like Exec, but panics if an error occurs.
+func (_d *PromoCodeUsageDeleteOne) ExecX(ctx context.Context) {
+	if err := _d.Exec(ctx); err != nil {
+		panic(err)
+	}
+}