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>

index.html

@@ -166,22 +166,22 @@
         <div id="artist-songs-list"></div>
       </div>
 
-      <!-- ITUNES ALBUM DETAIL -->
-      <div class="page" id="page-itunes-album-detail">
-        <button class="back-btn" id="itunes-album-back-btn"><svg width="13" height="13" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><polyline points="15 18 9 12 15 6"/></svg>Zurück</button>
+      <!-- DEEZER ALBUM DETAIL -->
+      <div class="page" id="page-deezer-album-detail">
+        <button class="back-btn" id="deezer-album-back-btn"><svg width="13" height="13" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><polyline points="15 18 9 12 15 6"/></svg>Zurück</button>
         <div class="album-header">
-          <div class="album-cover" id="itunes-album-cover-wrap"><div class="no-art">💿</div></div>
+          <div class="album-cover" id="deezer-album-cover-wrap"><div class="no-art">💿</div></div>
           <div class="album-meta">
             <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>
+            <div class="album-name" id="deezer-album-detail-name">—</div>
+            <div class="album-artist-name" id="deezer-album-detail-artist"></div>
+            <div class="album-stats" id="deezer-album-detail-stats"></div>
             <div class="album-actions">
-              <button class="btn-outline" id="itunes-album-dl-btn"><svg width="13" height="13" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path d="M21 15v4a2 2 0 0 1-2 2H5a2 2 0 0 1-2-2v-4"/><polyline points="7 10 12 15 17 10"/><line x1="12" y1="15" x2="12" y2="3"/></svg>Album laden</button>
+              <button class="btn-outline" id="deezer-album-dl-btn"><svg width="13" height="13" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path d="M21 15v4a2 2 0 0 1-2 2H5a2 2 0 0 1-2-2v-4"/><polyline points="7 10 12 15 17 10"/><line x1="12" y1="15" x2="12" y2="3"/></svg>Album laden</button>
             </div>
           </div>
         </div>
-        <div id="itunes-album-songs"></div>
+        <div id="deezer-album-songs"></div>
       </div>
 
       <!-- PARTIAL ALBUM DETAIL (incomplete album: downloaded + missing tracks) -->
@@ -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">Deezer</span>
+          <span class="badge badge-deezer" 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">Deezer Charts</span>
+          <span class="badge badge-deezer" 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>