UPLOAD a BUNDLE (multiple files, e.g. a website):
   POST https://skale.dev/throway/   with multipart/form-data containing 2+ file parts.
   -> Returns JSON: id, url, bundle:true, files:[{name,url,size,content_type}...].
   The bundle URL serves index.html inline (or a zip for agents).
   Each file is reachable at https://skale.dev/throway/<id>/<filename>.