feat: move the whole metadata/search stack from iTunes to Deezer (1.3)

Apple's iTunes /search returns 403 from server/datacenter IPs, which had broken global
search, charts, album/artist/single downloads and the metadata-editor autofill in
production. Everything now sources metadata from Deezer (free, no key, more requests,
returns explicit versions + real artist images + durations). Web + Android share one
source, so an artist resolves to one consistent name everywhere. Deezer results are
mapped to the legacy "ItunesItem" shape, so the UI + download flow are unchanged.

Backend:
- New backend/lib/deezer.js: lookupTrackMeta, fetchAlbumTracks, searchAlbumTracks,
  fetchArtistAlbums (+ pure pickTrackMatch/mapAlbumTrack for tests).
- metadata.js drops the iTunes lookups; novasonic-server download paths (track, album,
  artist, playlist enrich, spotify artwork) + autofill now use Deezer.
- Artist download uses Deezer discography (real albums only), not the iTunes album search.
- Editor autofill endpoint /api/itunes/lookup -> /api/meta/lookup; removed the dead
  iTunes /search proxy and the Apple charts RSS proxy.
- backend/test/deezer.test.js: unit tests for numbering, mixed-artist album-artist
  stability, explicit flags, the Japanese-title match guard (npm test; RUN_LIVE=1 for live).

Web:
- api.js search/lookups already on Deezer; charts now use Deezer /chart. Artist cards
  show the real Deezer photo. Visible "iTunes"/"Apple Music" labels -> "Deezer"
  (search badge, charts badge, preview bar, editor button, artist heading). SW ns-v51.

Android:
- New DeezerModels.kt with Dz* models + mappers to ItunesItem/ItunesRssEntry.
- ItunesClient is Deezer-backed (search = tracks+albums+artists in parallel; album/artist
  lookups; /chart charts), same method signatures. Visible strings -> Deezer.

Docs: README, CLAUDE.md and CHANGELOG (1.3) updated; Platform Parity Matrix reflects the
shared Deezer source + Android non-local artist page.

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

src/ui/metadata.js

@@ -207,18 +207,18 @@ export async function autofillMusicBrainz() {
   }
 }
 
-export async function autofillItunes() {
+export async function autofillDeezer() {
   if (!S.cfg.backendUrl) { toast('⚠ Kein Backend konfiguriert'); return; }
   const s = S.infoSong;
   if (!s) return;
   const artist = document.getElementById('ie-artist').value || s.artist || '';
   const title  = document.getElementById('ie-title').value  || s.title  || '';
   const status = document.getElementById('info-edit-status');
-  status.textContent = '🔍 Apple Music…';
+  status.textContent = '🔍 Deezer…';
   try {
-    const r = await fetch(`${S.cfg.backendUrl}/api/itunes/lookup?artist=${encodeURIComponent(artist)}&title=${encodeURIComponent(title)}`);
+    const r = await fetch(`${S.cfg.backendUrl}/api/meta/lookup?artist=${encodeURIComponent(artist)}&title=${encodeURIComponent(title)}`);
     const d = await r.json();
-    if (!d.found) { status.textContent = '❌ Kein Treffer auf iTunes'; return; }
+    if (!d.found) { status.textContent = '❌ Kein Treffer auf Deezer'; return; }
     if (d.title)       document.getElementById('ie-title').value       = d.title;
     if (d.artist)      document.getElementById('ie-artist').value      = _fmtArtists(d.artist, '; ');
     if (d.albumArtist) document.getElementById('ie-albumartist').value = _fmtArtists(d.albumArtist, ', ');
@@ -232,9 +232,9 @@ export async function autofillItunes() {
       S._infoArtData = { url: d.coverUrl };
       document.getElementById('info-edit-art-preview').innerHTML =
         `<img src="${d.coverUrl}" style="width:100%;height:100%;object-fit:cover" onerror="this.parentNode.innerHTML='<div class=\\'no-art\\' style=\\'width:100%;height:100%;display:flex;align-items:center;justify-content:center;font-size:28px\\'>🎵</div>'">`;
-      status.textContent = '✅ Metadaten + Cover von Apple Music';
+      status.textContent = '✅ Metadaten + Cover von Deezer';
     } else {
-      status.textContent = '✅ Metadaten von Apple Music (kein Cover)';
+      status.textContent = '✅ Metadaten von Deezer (kein Cover)';
     }
   } catch (e) {
     status.textContent = '❌ Fehler: ' + e.message;