Names quak builds from server data fit in 255 bytes (closes #205)

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

TODO.md

@@ -17,15 +17,26 @@ pre-1.0
 
 # Next Step
 
-One bug is open: https://git.eeqj.de/sneak/quak/issues/205. The check of quak
-against a live Ente account, https://git.eeqj.de/sneak/quak/issues/187, needs an
-account only sneak has, so it waits on him.
+No bug is open. The check of quak against a live Ente account,
+https://git.eeqj.de/sneak/quak/issues/187, needs an account only sneak has, so
+it waits on him.
 
 Tagging and releases are decided by sneak alone, and happen only when he
 declares one.
 
 # Completed Steps
 
+- 2026-10-18: Names quak builds from an album name or a title fit in a file name
+  (issue 205). `shortenKeepingExtension` in `src/filename.ts` cuts a name short
+  to a number of bytes, keeping its extension when it fits, and can put text
+  right before the extension; the backup's `withID` uses it for an ID. The
+  default names of `quak get`, `quak get-thumb`, `downloadFile` and
+  `downloadThumbnail` are cut short with it to 255 bytes, `thumb_` included.
+  `backup-metadata` cuts an album's name short so that its folder,
+  `<id>-<name>`, fits in 255 bytes. `safeExtension` gives `.bin` for an
+  extension of more than 16 letters and digits, so a save path's name always
+  fits.
+
 - 2026-10-16: ML data the server sends that does not decrypt, gunzip or parse is
   no longer taken for no ML data (issue 198). `fetchMLDataBatch` returns why for
   each such file beside the payloads; ML data that parses to something other