fix: sync native track index before opening Now Playing overlay

On Android, onTrackChanged fires asynchronously so opening the overlay
quickly after a track change could show the previous song. Query
NSBridge.getState() synchronously at open time to get the real index.
Same flash can also occur on web — openNowPlaying now always renders
from current S.qIdx.

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

src/nowplaying.js

@@ -8,6 +8,15 @@ import { openPlModal, showSongInfo } from './ui.js';
 
 // ─── NOW PLAYING OVERLAY ───
 export function openNowPlaying() {
+  // On Android, onTrackChanged is async — query native for the current index
+  // before rendering so we never show the previous song for a flash.
+  if (typeof window.NSBridge !== 'undefined') {
+    try {
+      const state = JSON.parse(window.NSBridge.getState() || '{}');
+      if (typeof state.currentIndex === 'number' && state.currentIndex >= 0 && state.currentIndex < S.queue.length)
+        S.qIdx = state.currentIndex;
+    } catch {}
+  }
   S.npOpen = true;
   const overlay = document.getElementById('np-overlay');
   overlay.classList.add('open');