Revert "experiment(web): drop separate preload <audio> element (single-element like Navidrome)"

This reverts commit f252586398.

src/player/player.js

@@ -293,11 +293,14 @@ function _preloadNext() {
   const ni = _nextIdx();
   if(ni < 0) return;
   const next = S.queue[ni];
-  if(!next) return;
+  if(!next || _preId === next.id) return;
-  // (b) EXPERIMENT — no separate preload <audio> element. Navidrome's player keeps a single
+  _preId  = next.id;
-  // element only; a second buffering media element appears to make Chromium flip the OS media
+  _preUrl = streamUrl(next.id);
-  // session on skip (Windows tile flicker). We rely on the main element's preload="auto" + the
+  // Real Audio preload — actually buffers the stream so canplay fires instantly
-  // browser HTTP cache instead, and just warm the next cover art. Easy to revert if it doesn't help.
+  if(_preAudio) { _preAudio.src = ''; _preAudio = null; }
+  _preAudio = new Audio();
+  _preAudio.preload = 'auto';
+  _preAudio.src = _preUrl;
   if(next.coverArt) {
     [256, 512, 1024].forEach(size => {
       const img = new Image();