feat(ui): display livePartial / transcript_delta in ChatBubble as 'Hearing:' indicator

- REST STT now sends delta (full text) so UI lights up immediately with what was heard.
- Works as 'live' for the final transcript (true partials would stream words if Realtime was available).
- Per PLAN item 3.

frontend/src/App.tsx

@@ -28,6 +28,7 @@ export default function App() {
     sendText,
     startRecording,
     stopRecording,
+    livePartial,
   } = useConversation();
 
   const [currentSceneId, setCurrentSceneId] = useState('cozy-room');
@@ -143,7 +144,7 @@ export default function App() {
 
             {/* Column 3: Chat + Text Input */}
             <div className="space-y-4">
-              <ChatBubble messages={messages} isKiraSpeaking={isKiraSpeaking} userName={userName} />
+              <ChatBubble messages={messages} isKiraSpeaking={isKiraSpeaking} userName={userName} livePartial={livePartial} />
 
               {/* Text input fallback */}
               <div className="glass-card p-3">