fix(web): 'Unknown Artist' download from artist page + rename itunes*→deezer* identifiers

Fix (the reported bug):
- Deezer's /artist/{id}/albums omits the artist object, so discography album cards had an
  empty artist name → the download modal fell back to the literal "Unknown Artist", which
  poisoned the yt-dlp search ("Unknown Artist <album>") and its artist/channel filter, failing
  with "Nicht eindeutig gefunden".
- deezerLookupArtistAlbums now backfills the known artist name (we're on that artist's page).
- openDlModal now defaults album cards to an ALBUM download (was always Track), so a one-click
  download no longer grabs an album as a single track named after the album.

Rename (requested cleanup, dependency-checked so nothing breaks):
- All frontend itunes* identifiers → deezer* (functions, the ItunesItem-shape field keys
  itunesData/itunesArtistId/itunesFanCount/itunesId, the itunes-album-detail route + DOM ids,
  the badge-itunes CSS class). The backend reads none of these fields, so the boundary is safe.
- Verified: build passes; route/DOM-id/CSS producer↔consumer all consistent; only the factual
  "Apple's iTunes /search 403" comments keep the historical name. SW ns-v62.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

styles.css

@@ -209,7 +209,7 @@ nav{flex:1;overflow-y:auto;padding:4px 10px}
 /* ── BADGES ── */
 .badge{display:inline-flex;align-items:center;gap:4px;font-size:10px;font-weight:600;padding:3px 8px;border-radius:20px;letter-spacing:.3px}
 .badge-new{background:var(--blue-dim);color:var(--blue)}
-.badge-itunes{background:rgba(252,100,100,.12);color:#fc6464}
+.badge-deezer{background:rgba(252,100,100,.12);color:#fc6464}
 .badge-local{background:var(--green-dim);color:var(--green)}
 
 /* ── GLOBAL SEARCH RESULTS ── */