fix(web): Deezer artist images + rename the search label

- Search artist cards now use the Deezer artist picture directly (Deezer artists carry
  a photo, unlike iTunes entities) instead of a null image + an extra album lookup;
  the lookup stays only as a fallback when no picture is present.
- Non-local (Deezer) artist pages: fetch the Deezer artist picture (/artist/{id}) for
  the hero photo, which was blank because getArtistImage only runs for Navidrome artists.
- Label "iTunes Künstler" → "Deezer Künstler".

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

public/sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'ns-v49';
+const CACHE = 'ns-v50';
 const PRECACHE = ['/', 'index.html', 'manifest.json', 'icon.svg'];
 const SKIP_PATHS = ['/rest/stream', '/rest/download', '/config.js'];
 // Auth token params stripped from cache keys so artwork survives across sessions/token refreshes.