feat: smooth progress bar scrubbing with touch drag support

- initProgressScrub() adds touchstart/move/end + mousedown drag to both
  the player bar and NP overlay progress bars
- CSS transition disabled during scrub so fill follows finger instantly
- updateProgress() skips DOM updates while _scrubbing is active so
  timeupdate events don't fight the drag position
- Works on both bars with a shared _initBarScrub helper

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

app.js

@@ -122,6 +122,7 @@ window.addEventListener('load',()=>{
   previewAudio.addEventListener('ended',stopPreview);
   audio.volume=0.8;
   injectPWA();
+  initProgressScrub();
   // Now Playing: click player-art to open
   const pa=document.getElementById('player-art');
   if(pa)pa.addEventListener('click', openNowPlaying);
@@ -1057,7 +1058,7 @@ function expandArtistBio(){
   if(el&&window._artistBioFull)el.textContent=window._artistBioFull;
 }
 function updateProgress(){
-  if(!audio.duration)return;
+  if(!audio.duration||_scrubbing)return;
   syncMediaSessionPosition();
   const p=(audio.currentTime/audio.duration)*100;
   document.getElementById('progress-fill').style.width=p+'%';
@@ -1074,6 +1075,41 @@ function updateProgress(){
   }
 }
 function seekTo(e){const bar=document.getElementById('progress-bar');const rect=bar.getBoundingClientRect();audio.currentTime=((e.clientX-rect.left)/rect.width)*audio.duration}
+
+let _scrubbing=false;
+function initProgressScrub(){
+  _initBarScrub(
+    document.getElementById('progress-bar'),
+    document.getElementById('progress-fill'),
+    pos=>{
+      document.getElementById('time-cur').textContent=formatDur(pos*audio.duration);
+    }
+  );
+  _initBarScrub(
+    document.getElementById('np-bar'),
+    document.getElementById('np-fill'),
+    pos=>{
+      const el=document.getElementById('np-cur');
+      if(el)el.textContent=formatDur(pos*audio.duration);
+    }
+  );
+}
+function _initBarScrub(bar,fill,onMove){
+  if(!bar||!fill)return;
+  function getPos(clientX){const r=bar.getBoundingClientRect();return Math.max(0,Math.min(1,(clientX-r.left)/r.width));}
+  function startScrub(pos){_scrubbing=true;fill.style.transition='none';fill.style.width=(pos*100)+'%';onMove(pos);}
+  function moveScrub(pos){fill.style.width=(pos*100)+'%';onMove(pos);}
+  function endScrub(pos){_scrubbing=false;fill.style.transition='';if(audio.duration)audio.currentTime=pos*audio.duration;}
+  bar.addEventListener('touchstart',e=>{startScrub(getPos(e.touches[0].clientX));e.stopPropagation();},{passive:true});
+  bar.addEventListener('touchmove',e=>{if(_scrubbing)moveScrub(getPos(e.touches[0].clientX));},{passive:true});
+  bar.addEventListener('touchend',e=>{if(_scrubbing)endScrub(getPos(e.changedTouches[0].clientX));},{passive:true});
+  bar.addEventListener('mousedown',e=>{
+    startScrub(getPos(e.clientX));e.preventDefault();
+    const mm=e2=>{if(_scrubbing)moveScrub(getPos(e2.clientX));};
+    const mu=e2=>{if(_scrubbing)endScrub(getPos(e2.clientX));document.removeEventListener('mousemove',mm);document.removeEventListener('mouseup',mu);};
+    document.addEventListener('mousemove',mm);document.addEventListener('mouseup',mu);
+  });
+}
 function setVolume(v){audio.volume=v/100;previewAudio.volume=v/100}
 
 // ─── STAR ───
@@ -1610,11 +1646,7 @@ function npToggleStar() {
     .catch(e => toast('Fehler: ' + e.message));
 }
 
-function npSeek(e) {
-  const bar = document.getElementById('np-bar');
-  const rect = bar.getBoundingClientRect();
-  audio.currentTime = ((e.clientX - rect.left) / rect.width) * audio.duration;
-}
+function npSeek(e){}
 
 let npQueueMode = false;
 function switchNpTab(tab) {