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/state.js

@@ -1,6 +1,6 @@
 // Shared mutable state — imported as { S } in every module
 export const S = {
-  cfg: { url: '', user: '', pass: '', lastfmKey: '', backendUrl: '' },
+  cfg: { url: '', user: '', pass: '', lastfmKey: '', backendUrl: '', showPlayCount: false },
 
   // Playback
   queue: [],