fix: instant OS notification update + real audio preload for gapless playback

- Call updateMediaSession immediately on track change so skip buttons and
  cover art in the OS notification bar update without waiting for audio load
- Replace link[rel=prefetch] (no-op for audio streams) with a shadow Audio
  element (preload=auto) that actually buffers the next track
- Start preloading 60s before track end instead of 30s for more buffer margin

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

src/player/player.js

@@ -273,10 +273,10 @@ function _setAudioSession() {
   try { if(navigator.audioSession) navigator.audioSession.type = 'playback'; } catch {}
 }
 
-// ─── PRELOAD (resource hint keeps connection open through Doze gap) ───────
+// ─── PRELOAD — shadow Audio element actually buffers the next track ──────────
-let _preUrl  = '';
+let _preUrl   = '';
-let _preId   = '';
+let _preId    = '';
-let _preLink = null;
+let _preAudio = null;
 
 function _nextIdx() {
   if(S.repeat === 'one') return S.qIdx;
@@ -286,19 +286,18 @@ function _nextIdx() {
 }
 
 function _preloadNext() {
-  if (HAS_BRIDGE) return; // ExoPlayer handles buffering natively
+  if (HAS_BRIDGE) return;
   const ni = _nextIdx();
   if(ni < 0) return;
   const next = S.queue[ni];
   if(!next || _preId === next.id) return;
   _preId  = next.id;
   _preUrl = streamUrl(next.id);
-  if(_preLink) _preLink.remove();
+  // Real Audio preload — actually buffers the stream so canplay fires instantly
-  _preLink = document.createElement('link');
+  if(_preAudio) { _preAudio.src = ''; _preAudio = null; }
-  _preLink.rel  = 'prefetch';
+  _preAudio = new Audio();
-  _preLink.as   = 'fetch';
+  _preAudio.preload = 'auto';
-  _preLink.href = _preUrl;
+  _preAudio.src = _preUrl;
-  document.head.appendChild(_preLink);
   if(next.coverArt) {
     [256, 512, 1024].forEach(size => {
       const img = new Image();
@@ -309,7 +308,7 @@ function _preloadNext() {
 
 function _clearPreload() {
   _preId = ''; _preUrl = '';
-  if(_preLink) { _preLink.remove(); _preLink = null; }
+  if(_preAudio) { _preAudio.src = ''; _preAudio = null; }
 }
 
 // ─── PLAY HISTORY (for prev-in-shuffle) ──────────────────────────────────────
@@ -388,6 +387,7 @@ export function playCurrent() {
   _resetProgressUI();
   if(navigator.mediaSession) navigator.mediaSession.playbackState = 'playing';
   updatePlayerUI(s, true);
+  updateMediaSession(s);
   onNpSongChange(s.id);
   renderQueue();
   _scheduleScrobble(s.id, s.duration);
@@ -830,7 +830,7 @@ export function updateProgress() {
   if(!S.audio.duration || S._scrubbing) return;
   syncMediaSessionPosition();
   const rem = S.audio.duration - S.audio.currentTime;
-  if(rem > 0 && rem < 30 && !S._trackChanging) _preloadNext();
+  if(rem > 0 && rem < 60 && !S._trackChanging) _preloadNext();
   const p = (S.audio.currentTime / S.audio.duration) * 100;
   document.getElementById('progress-fill').style.width = p + '%';
   document.getElementById('time-cur').textContent   = formatDur(S.audio.currentTime);