fix: await unmute() to ensure VAD reinitializes before continuing

The unmute() function in the JS SDK is async because it needs to
reinitialize VAD. Not awaiting it could cause race conditions where
user speech isn't detected immediately after unmuting.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: jackbridger

src/index.tsx

@@ -320,12 +320,12 @@ const useLayercodeAgent = (
     clientRef.current.mute();
   }, []);
 
-  const unmute = useCallback(() => {
+  const unmute = useCallback(async () => {
     if (!clientRef.current) {
       console.warn('[Layercode] unmute() called but no client exists. Did you call connect() first?');
       return;
     }
-    clientRef.current.unmute();
+    await clientRef.current.unmute();
   }, []);
 
   const setAudioInput = useCallback(