Add voice error handling - speak errors aloud and continue session

Previously: API errors were silent, session stopped, user confused
Now: Julia speaks error message, adds to transcript, keeps listening

Changes:
- Catch block now speaks error via TTS: "Sorry, I encountered an error: [msg]"
- Error added to transcript (visible in chat history)
- Session continues in listening state (doesn't stop on error)
- User can try again immediately without restarting session

UX improvement: graceful error recovery instead of silent failure

contexts/VoiceContext.tsx:332-351

contexts/VoiceContext.tsx

@@ -335,10 +335,24 @@ export function VoiceProvider({ children }: { children: ReactNode }) {
           console.log('[VoiceContext] API request aborted');
           return null;
         }
+
+        // Handle API errors gracefully with voice feedback
         const errorMsg = err instanceof Error ? err.message : 'Unknown error';
         console.warn('[VoiceContext] API error:', errorMsg);
+
+        // Create user-friendly error message for TTS
+        const spokenError = `Sorry, I encountered an error: ${errorMsg}. Please try again.`;
+
+        // Add error to transcript for chat display
+        addTranscriptEntry('assistant', spokenError);
+
+        // Speak the error message
+        await speak(spokenError);
+
+        // Don't set status to idle - return to listening after speaking error
+        // This keeps the voice session active
+
         setError(errorMsg);
-        setStatus('idle');
         return null;
       }
     },