One album or file quak cannot decrypt no longer stops a refresh or a backup (closes #181)

A file or album whose key, metadata or name does not decrypt used to
throw out of the refresh, so quak backup stopped before storing
anything, every run. Client.collectionsSince and filesSince now return
such a row in undecryptable with the reason, the refresh leaves it out,
and the store keeps the list in metadata.json until a later refresh
decrypts or deletes the record. lib.backup() records each such file in
failures.json unless a copy in another album decrypted, in which case it
stores the original from that copy. Each such album is listed in
BackupResult.undecryptableAlbums and printed as one FAILED album line.
quak backup exits 1 while either remains. An album or file that no
longer decrypts loses its album folder, JSON and links; its original
stays.

Model: opus-5-5

TODO.md

@@ -25,6 +25,19 @@ declares one.
 
 # Completed Steps
 
+- 2026-10-14: An album or file quak cannot decrypt, or whose metadata is not
+  JSON, no longer fails the refresh, so one bad record no longer stops
+  `quak backup` from storing anything (issue 181). The refresh leaves it out, an
+  album with its files, and the library keeps it with the reason in
+  `metadata.json` until the server sends a copy that decrypts or deletes it.
+  `quak backup` stores every other file, records each such file in
+  `failures.json` with an error starting `could not be decrypted:`, names each
+  such album's ID in a printed line, or with `--json` in `undecryptableAlbums`,
+  and exits 1 while any remain. A file whose copy in another album decrypts is
+  not recorded: its original is stored from that copy, and the album where it
+  does not decrypt neither links nor lists it. The read commands answer from
+  what decrypted.
+
 - 2026-10-14: `quak backup` no longer asks the server for changes every 3
   seconds while it runs (issue 183). It opens its library with
   `refreshIntervalSeconds: Infinity`, which the library now takes as no