feat: add screen share audio support

Pass audio: true to setScreenShareEnabled so the browser offers the
"Share audio" checkbox. Track ScreenShareAudio from remote participants
and play it through a dedicated audio element with the same volume
pipeline (including boost >100%).

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

@@ -96,7 +96,11 @@ export function VoiceControlBar() {
     const room = getActiveRoom();
     if (!room) return;
     try {
-      await room.localParticipant.setScreenShareEnabled(!isScreenSharing);
+      if (!isScreenSharing) {
+        await room.localParticipant.setScreenShareEnabled(true, { audio: true });
+      } else {
+        await room.localParticipant.setScreenShareEnabled(false);
+      }
       toggleScreenShare();
     } catch (err) {
       console.error('[VoiceControlBar] Failed to toggle screen share:', err);