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>

src/ui.js

@@ -59,6 +59,7 @@ export function openSettings() {
   document.getElementById('s-pass').value    = '';
   document.getElementById('s-lastfm').value       = S.cfg.lastfmKey        || '';
   document.getElementById('s-backend').value      = S.cfg.backendUrl       || '';
+  document.getElementById('s-show-playcount').classList.toggle('on', !!S.cfg.showPlayCount);
   _renderThemePicker();
   document.getElementById('settings-modal').classList.add('open');
   checkBackend();
@@ -91,6 +92,7 @@ export function saveSettings() {
   if(pass) S.cfg.pass = pass;
   S.cfg.lastfmKey        = document.getElementById('s-lastfm').value.trim();
   S.cfg.backendUrl       = document.getElementById('s-backend').value.trim().replace(/\/$/,'');
+  S.cfg.showPlayCount    = document.getElementById('s-show-playcount').classList.contains('on');
   localStorage.setItem('ns_cfg', JSON.stringify(S.cfg));
   closeSettings(); toast('✅ Gespeichert');
 }