fix: eliminate notification/playerbar song desync on Android

Two-pronged fix for the state drift between the system notification
(ground truth) and the WebView player bar:

JS (player.js): onTrackChanged now reconciles the incoming index with a
synchronous NSBridge.getState() call before applying it. Stale callbacks
from earlier rapid skips immediately correct themselves to the live
settled index instead of overwriting the correct state.

Kotlin (MusicService.kt): debounce JS-initiated transitions (seek /
setQueue) by 120 ms so rapid skip sequences produce one onTrackChanged
notification at the final index rather than one per skip step. Auto-advance
transitions are still fired immediately since JS doesn't initiate those.

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

src/player.js

@@ -143,9 +143,16 @@ window.NSPlayer = {
     try {
       const p = JSON.parse(payloadJson);
       if (typeof p.index !== 'number') return;
-      if (p.index < 0 || p.index >= S.queue.length) return;
-      const indexChanged = (p.index !== S.qIdx);
-      S.qIdx = p.index;
+      // Reconcile with the live native state so stale out-of-order callbacks
+      // (e.g. from rapid skips) don't overwrite the already-correct index.
+      let idx = p.index;
+      try {
+        const live = JSON.parse(window.NSBridge.getState() || '{}');
+        if (typeof live.currentIndex === 'number') idx = live.currentIndex;
+      } catch {}
+      if (idx < 0 || idx >= S.queue.length) return;
+      const indexChanged = (idx !== S.qIdx);
+      S.qIdx = idx;
       const s = S.queue[S.qIdx];
       if (!s) return;
       updatePlayerUI(s, true);