fix: Samsung notification stays alive; retry play() on background rejection

- Set playbackState='playing' explicitly before MediaMetadata swap so
  Samsung One UI never sees a gap where state is ambiguous during skip
- Add retry loop (500ms→1s→2s→4s→8s) in playCurrent() catch — handles
  Android Doze rejecting play() in background; stops retrying if the
  song changes mid-flight (AbortError)
- Fix error handler: set _trackChanging=true before audio.load() so
  the load()'s pause event can't slip past the Samsung notification guard

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

src/main.js

@@ -152,7 +152,12 @@ window.addEventListener('load', () => {
     _errRetries++;
     const delay = Math.min(1000 * Math.pow(2, _errRetries - 1), 8000); // 1s, 2s, 4s, 8s
     clearTimeout(_errTimer);
-    _errTimer = setTimeout(() => { S.audio.load(); S.audio.play().catch(() => {}); }, delay);
+    _errTimer = setTimeout(() => {
+      if(!S.queue[S.qIdx]) return;
+      S._trackChanging = true; // prevent load()'s pause event from dismissing Samsung notification
+      S.audio.load();
+      S.audio.play().catch(() => { S._trackChanging = false; });
+    }, delay);
   });
 
   S.audio.volume = 0.5;