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>

index.html

@@ -172,7 +172,7 @@
         <div class="album-header">
           <div class="album-cover" id="itunes-album-cover-wrap"><div class="no-art">💿</div></div>
           <div class="album-meta">
-            <div class="album-type">iTunes</div>
+            <div class="album-type">Deezer</div>
             <div class="album-name" id="itunes-album-detail-name">—</div>
             <div class="album-artist-name" id="itunes-album-detail-artist"></div>
             <div class="album-stats" id="itunes-album-detail-stats"></div>
@@ -333,7 +333,7 @@
       <div class="page" id="page-discover">
         <div class="page-header">
           <div class="page-title"><span class="blue">Global</span> Suche</div>
-          <span class="badge badge-itunes" style="font-size:11px;padding:4px 10px">iTunes Store</span>
+          <span class="badge badge-itunes" style="font-size:11px;padding:4px 10px">Deezer</span>
         </div>
         <div class="search-wrap" style="padding:0 0 20px">
           <div class="search-box" style="background:var(--surface);border-color:var(--border2)">
@@ -350,7 +350,7 @@
       <div class="page" id="page-new-releases">
         <div class="page-header">
           <div class="page-title">Neue <em>Releases</em></div>
-          <span class="badge badge-itunes" style="font-size:11px;padding:4px 10px">iTunes Charts</span>
+          <span class="badge badge-itunes" style="font-size:11px;padding:4px 10px">Deezer Charts</span>
         </div>
         <div class="section-header" style="margin-top:0"><span class="section-title">Top Alben weltweit</span></div>
         <div id="nr-albums" class="grid grid-4"></div>
@@ -545,12 +545,12 @@
   </button>
 </div>
 
-<!-- PREVIEW BAR (iTunes 30s) -->
+<!-- PREVIEW BAR (Deezer 30s) -->
 <div class="preview-bar" id="preview-bar">
   <div class="player-art" id="preview-art" style="width:42px;height:42px;border-radius:6px"><div class="no-art" style="font-size:16px">♪</div></div>
   <div class="preview-info">
     <div class="preview-title" id="preview-title">—<span class="preview-badge">30s Preview</span></div>
-    <div class="preview-sub" id="preview-sub">iTunes Store</div>
+    <div class="preview-sub" id="preview-sub">Deezer</div>
   </div>
   <div class="preview-prog"><div class="preview-fill" id="preview-fill"></div></div>
   <button class="preview-close" onclick="stopPreview()">✕</button>
@@ -996,9 +996,9 @@
           <svg width="11" height="11" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" style="margin-right:4px"><circle cx="11" cy="11" r="8"/><line x1="21" y1="21" x2="16.65" y2="16.65"/></svg>
           MusicBrainz
         </button>
-        <button class="btn-outline blue" style="font-size:11px;padding:6px 10px;height:fit-content" onclick="autofillItunes()">
+        <button class="btn-outline blue" style="font-size:11px;padding:6px 10px;height:fit-content" onclick="autofillDeezer()">
           <svg width="11" height="11" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" style="margin-right:4px"><circle cx="11" cy="11" r="8"/><line x1="21" y1="21" x2="16.65" y2="16.65"/></svg>
-          Apple Music
+          Deezer
         </button>
       </div>
       <div class="info-edit-fields">