Fix Android media notification: add setPositionState + seek handlers

- setPositionState synced every second via updateProgress so the notification shows progress bar and timestamps
- seekto handler enables dragging the notification progress bar
- seekbackward/seekforward handlers enable 10s skip buttons

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

app.js

@@ -987,6 +987,17 @@ function updateMediaSession(s){
   navigator.mediaSession.setActionHandler('pause',togglePlay);
   navigator.mediaSession.setActionHandler('previoustrack',prevSong);
   navigator.mediaSession.setActionHandler('nexttrack',nextSong);
+  navigator.mediaSession.setActionHandler('seekbackward',d=>{audio.currentTime=Math.max(0,audio.currentTime-(d.seekOffset||10))});
+  navigator.mediaSession.setActionHandler('seekforward',d=>{audio.currentTime=Math.min(audio.duration||0,audio.currentTime+(d.seekOffset||10))});
+  navigator.mediaSession.setActionHandler('seekto',d=>{if(d.seekTime!=null)audio.currentTime=d.seekTime});
+}
+let _msPosLast=0;
+function syncMediaSessionPosition(){
+  if(!navigator.mediaSession?.setPositionState||!audio.duration||isNaN(audio.duration))return;
+  const now=Date.now();
+  if(now-_msPosLast<1000)return;
+  _msPosLast=now;
+  try{navigator.mediaSession.setPositionState({duration:audio.duration,playbackRate:audio.playbackRate||1,position:Math.min(audio.currentTime,audio.duration)});}catch{}
 }
 function togglePlay(){if(audio.src)audio.paused?audio.play():audio.pause()}
 function setPlayIcon(playing){
@@ -1031,6 +1042,7 @@ function expandArtistBio(){
 }
 function updateProgress(){
   if(!audio.duration)return;
+  syncMediaSessionPosition();
   const p=(audio.currentTime/audio.duration)*100;
   document.getElementById('progress-fill').style.width=p+'%';
   document.getElementById('time-cur').textContent=formatDur(audio.currentTime);