Authenticated arbitrary file deletion via path traversal

Path traversal in BeikeShop 1.5.5 and earlier allows remote authenticated users to delete arbitrary server files through the admin file manager. FileManagerService::deleteFiles accepts traversal sequences in the files argument and resolves them outside the intended file-manager directory before deletion. Access to the administrative file-manager endpoint is required, and successful exploitation can remove any file writable by the web-server process, potentially interrupting the store.