feat(library): edit/fix album metadata

Correct an owned album's artist/album/year from the Library modal ("Edit
metadata"). PATCH /api/library/[id] renames the folder to the canonical
Artist/Album (Year) scheme on the /music mount, updates the LibraryItem,
and re-resolves the MusicBrainz release-group (cover art) when the
artist/album changed (best-effort — keeps the old rgMbid on an MB outage).

- New shared lib/library-path.ts (safeName, albumDir, yearFromPath); the
  manual-import route now uses it so edits and imports name folders
  identically.
- Library GET falls back to the folder's "(YYYY)" for the year when there's
  no matching release, so edited/manual years show in the grid.
- Does NOT rewrite embedded file tags (a worker/mutagen job) — Lyra reads
  from the folder + DB. Guards paths inside the library root; 409 on folder
  or (artist,album) collision.

web 172 tests.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/src/app/design.css

@@ -284,6 +284,7 @@ nav.contents .sep { flex: 1; }
   font-family: var(--mono); font-size: 0.64rem; letter-spacing: 0.12em; text-transform: uppercase; color: var(--accent);
 }
 .save-row { display: flex; align-items: center; gap: 14px; margin-top: 8px; }
+.edit-meta { display: flex; flex-direction: column; gap: 8px; width: 100%; }
 .settings-section { margin-bottom: 30px; }
 .help { font-size: 0.8rem; color: var(--graphite); line-height: 1.5; margin: 4px 0 14px; max-width: 62ch; }
 .help b { color: var(--ink); font-weight: 600; }