The default names of `quak get`, `quak get-thumb`, `downloadFile` and
`downloadThumbnail`, and the album folders of `backup-metadata`, could be
over 255 bytes, which a file system refuses. `shortenKeepingExtension` in
`src/filename.ts` cuts a name short, keeping its extension when it fits,
and can put text right before the extension; the backup's `withID` now
calls it instead of doing the same itself. The `get` defaults use it with
`thumb_` counted. A `backup-metadata` folder keeps its `<id>-` and has the
name after it cut short. `safeExtension` gives `.bin` for an extension of
more than 16 letters and digits, so a save path's name always fits.
Model: opus-5-5
sneak
fd40714a6d