feat: timer scrobble (12s), artist topsong star+menu, play count toggle

Scrobbling:
- Replace end-of-track scrobble with 12s timer approach
- Android: schedule on onTrackChanged, cancel on pause
- Web: schedule in playCurrent, cancel in togglePlay pause + onEnded
- Skip/new track resets the timer automatically (new song ID)

Artist top songs:
- Add star button and 3-dots context menu to every top song row
- Topsong grid expanded to 5 columns to fit action buttons

Settings — play count toggle:
- New "Bibliothek" section with toggle switch
- When on: shows play count in album/playlist song rows
- Artist page always shows play count regardless of toggle
- Persisted in ns_cfg localStorage

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

styles.css

@@ -219,6 +219,7 @@ button:focus{outline:none}
 .song-info .song-artist{font-size:11px;color:var(--text2);margin-top:1px}
 .song-meta{display:flex;align-items:center;gap:6px}
 .song-dur{font-size:11px;color:var(--text3);font-family:var(--mono)}
+.song-plays{font-size:11px;color:var(--text3);font-family:var(--mono)}
 .song-actions{display:flex;gap:2px;opacity:0;transition:opacity .15s}
 .song-item:hover .song-actions{opacity:1}
 @media (hover:none),(pointer:coarse){.song-actions{opacity:1}}
@@ -768,7 +769,7 @@ button:focus{outline:none}
 #spotify-enrich-status{display:flex;align-items:center;gap:8px;font-size:12px;color:var(--text2);padding:8px 12px;margin-bottom:8px;background:var(--surface);border:1px solid var(--border2);border-radius:8px;transition:opacity .4s}
 #spotify-enrich-status.done{color:var(--accent)}
 #spotify-enrich-status .enrich-spinner{width:12px;height:12px;border:2px solid var(--border2);border-top-color:var(--accent);border-radius:50%;animation:spin .7s linear infinite;flex-shrink:0}
-.topsong-item{display:grid;grid-template-columns:28px 44px 1fr auto;align-items:center;gap:10px;padding:7px 10px;border-radius:8px;cursor:pointer;transition:background .15s}
+.topsong-item{display:grid;grid-template-columns:28px 44px 1fr auto auto;align-items:center;gap:10px;padding:7px 10px;border-radius:8px;cursor:pointer;transition:background .15s}
 .topsong-item:hover{background:var(--surface)}
 .topsong-num{font-size:11px;color:var(--text3);font-family:var(--mono);text-align:center}
 .topsong-thumb{width:44px;height:44px;border-radius:6px;overflow:hidden;background:var(--surface2)}