Add YT/local audio toggle in pause menu for comparison

For songs with YouTube config, a YT: ON/OFF button appears in the pause
menu next to KB. Toggling it recreates the audio player so you can
compare YouTube vs local audio during the same session.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/pages/GamePage.module.css

@@ -165,6 +165,10 @@
   left: 72px;
 }
 
+.cornerBtnLeft3 {
+  left: 140px;
+}
+
 .cornerBtnRight {
   right: 16px;
   font-size: 18px;

src/pages/GamePage.tsx

@@ -70,6 +70,7 @@ export function GamePage() {
   const [audioPlayer, setAudioPlayer] = useState<AudioPlayer | null>(null)
   const ytHostRef = useRef<HTMLDivElement>(null)
   const [keyboardMode, setKeyboardMode] = useState(false)
+  const [useYoutube, setUseYoutube] = useState(!!resolvedSong.youtubeVideoId)
 
   // Load chart
   useEffect(() => {
@@ -93,7 +94,7 @@ export function GamePage() {
     let destroyed = false
     let player: AudioPlayer | null = null
 
-    if (resolvedSong.youtubeVideoId && ytHostRef.current) {
+    if (useYoutube && resolvedSong.youtubeVideoId && ytHostRef.current) {
       gameLog(`creating YouTube audio player: ${resolvedSong.youtubeVideoId} offset=${resolvedSong.youtubeOffset}`)
       createYouTubeAudioPlayer({
         videoId: resolvedSong.youtubeVideoId,
@@ -116,7 +117,7 @@ export function GamePage() {
       player?.destroy()
       setAudioPlayer(null)
     }
-  }, [resolvedSong.id])
+  }, [resolvedSong.id, useYoutube])
 
   // Pose detection (disabled in keyboard mode)
   const { loading, error, calibrationStatus, framingHint, gesture } = usePoseLoop(
@@ -348,6 +349,17 @@ export function GamePage() {
           >
             {keyboardMode ? 'KB: ON' : 'KB: OFF'}
           </button>
+          {resolvedSong.youtubeVideoId && (
+            <button
+              className={`${styles.cornerBtn} ${styles.cornerBtnLeft3}`}
+              onClick={() => {
+                playSound(SFX_BUTTON_DEFAULT)
+                setUseYoutube((v) => !v)
+              }}
+            >
+              {useYoutube ? 'YT: ON' : 'YT: OFF'}
+            </button>
+          )}
           {canFullscreen && !isFullscreen && (
             <button
               className={`${styles.cornerBtn} ${styles.cornerBtnRight}`}