Deluan 35d08a25a3 fix(album): don't wipe covers on album merges; bust disc/song art caches
Adversarial review findings:

- CopyAttributes copied uploaded_image/cover_art_updated_at unconditionally,
  so merging an album without a cover into one with a cover (retag onto an
  existing album ID, or phase-2 moved-track matching) blanked the
  destination's uploaded cover. Skip empty/NULL source values, mirroring the
  created_at guard, and make the mock faithful to the same semantics.

- The disc and mediafile artwork readers did not fold cover_art_updated_at
  into their cache keys, so song/disc art reached through the fromAlbum
  fallback kept serving stale bytes after a cover upload or delete.

- The UI cover cache-buster compared timestamps lexicographically; mixed
  offset/fractional formats could pick the older one. Compare as dates.
2026-07-17 21:34:15 -04:00
..
2024-05-24 20:19:26 -04:00
2026-05-28 22:13:05 -03:00
2026-05-28 22:13:05 -03:00