A page served by the gateway that signs in with the Pithos key file
(Ed25519 in Web Crypto) or an Export JSON S3 key, then browses, views,
downloads, uploads, renames and deletes, encrypting and decrypting in the
page with the same formats as the desktop. Checked against a local
gateway and real s3d: files the desktop encrypted open byte-identical in
the browser, and browser uploads open in the desktop client; the server
only ever holds encrypted names. Remember on this device keeps the key
sealed with a passphrase in IndexedDB.
