feat(subscription): 订阅过期状态自动更新与服务端排序

- 新增 SubscriptionExpiryService 定时任务，每分钟更新过期订阅状态
- 订阅列表支持服务端排序（按过期时间、状态、创建时间）
- 实时显示正确的过期状态，无需等待定时任务
- 允许对已过期订阅进行续期操作
- DataTable 组件支持 serverSideSort 模式

backend/internal/server/api_contract_test.go

@@ -1176,7 +1176,7 @@ func (r *stubUserSubscriptionRepo) ListActiveByUserID(ctx context.Context, userI
 func (stubUserSubscriptionRepo) ListByGroupID(ctx context.Context, groupID int64, params pagination.PaginationParams) ([]service.UserSubscription, *pagination.PaginationResult, error) {
 	return nil, nil, errors.New("not implemented")
 }
-func (stubUserSubscriptionRepo) List(ctx context.Context, params pagination.PaginationParams, userID, groupID *int64, status string) ([]service.UserSubscription, *pagination.PaginationResult, error) {
+func (stubUserSubscriptionRepo) List(ctx context.Context, params pagination.PaginationParams, userID, groupID *int64, status, sortBy, sortOrder string) ([]service.UserSubscription, *pagination.PaginationResult, error) {
 	return nil, nil, errors.New("not implemented")
 }
 func (stubUserSubscriptionRepo) ExistsByUserIDAndGroupID(ctx context.Context, userID, groupID int64) (bool, error) {