feat: Voice UI overhaul — fix black tiles, focus mode, track lifecycle

- Fix black screen when streams end by checking track readyState === 'live'
- Add track 'ended' event listeners in VoiceUser for immediate fallback to avatar
- Add visible "Grid" button to exit focus mode (replaces undiscoverable double-click)
- Auto-focus screen sharers, auto-unfocus when they stop sharing
- Add LIVE badge, speaking glow shadow, screen share object-contain
- Add TrackMuted/TrackUnmuted/ActiveSpeakersChanged Room events
- Fix PiP video attachment with shouldShow dependency

packages/web/src/components/voice/PictureInPicture.tsx

@@ -118,6 +118,7 @@ export function PictureInPicture() {
   }, [currentVoiceChannelId, channels]);
 
   // Video track attachment
+  // shouldShow in deps ensures re-run when PiP becomes visible (videoRef was null before)
   useEffect(() => {
     const videoEl = videoRef.current;
     if (!videoEl) return;
@@ -126,7 +127,7 @@ export function PictureInPicture() {
     } else {
       videoEl.srcObject = null;
     }
-  }, [selectedStream?.track]);
+  }, [selectedStream?.track, shouldShow]);
 
   // Initialize position to bottom-right
   useEffect(() => {