Extend speaking indicator duration to cover STT restart delay

User feedback: green speaker indicator was turning off too early,
creating an awkward visual gap during the 300ms audio focus delay.

Changes:
- Added 300ms delay to setIsSpeaking(false) in TTS onDone callback
- Keeps green "Speaking" indicator on until STT actually starts recording
- onError and onStopped still turn off immediately (user interruption)
- Smooth visual transition: TTS ends → 300ms delay → STT starts

UX improvement: eliminates the brief "nothing is happening" moment
between Julia finishing speech and microphone starting to listen.

contexts/VoiceContext.tsx:393

contexts/VoiceContext.tsx

@@ -386,7 +386,11 @@ export function VoiceProvider({ children }: { children: ReactNode }) {
         },
         onDone: () => {
           console.log('[VoiceContext] TTS completed');
-          setIsSpeaking(false);
+          // Delay turning off green indicator to match STT restart delay (300ms)
+          // This keeps the visual indicator on during the transition period
+          setTimeout(() => {
+            setIsSpeaking(false);
+          }, 300);
           // Return to listening state after speaking (if session wasn't stopped)
           if (!sessionStoppedRef.current) {
             setStatus('listening');
@@ -395,6 +399,7 @@ export function VoiceProvider({ children }: { children: ReactNode }) {
         },
         onError: (error) => {
           console.warn('[VoiceContext] TTS error:', error);
+          // On error, turn off indicator immediately (no delay)
           setIsSpeaking(false);
           if (!sessionStoppedRef.current) {
             setStatus('listening');
@@ -403,6 +408,7 @@ export function VoiceProvider({ children }: { children: ReactNode }) {
         },
         onStopped: () => {
           console.log('[VoiceContext] TTS stopped (interrupted)');
+          // When interrupted by user, turn off indicator immediately
           setIsSpeaking(false);
           // Don't set status to listening if session was stopped by user
           if (!sessionStoppedRef.current) {