feat: LiveKit AI answering agent (Gemini 2.5 Flash native audio)

- Hospital receptionist agent "Helix" with Gemini realtime speech-to-speech
- Tools wired to platform: lookupDoctor, bookAppointment, collectLeadInfo, transferToAgent
- Loads hospital context (doctors, departments) from platform GraphQL on startup
- Connects to LiveKit Cloud, joins rooms when participants connect
- Silero VAD for voice activity detection
- @livekit/agents + @livekit/agents-plugin-google + @livekit/agents-plugin-silero

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/supervisor/supervisor.service.ts

@@ -77,6 +77,7 @@ export class SupervisorService implements OnModuleInit {
     private mapOzonetelAction(action: string, eventData: string): AgentOzonetelState | null {
         switch (action) {
             case 'release': return 'ready';
+            case 'IDLE': return 'ready'; // agent available after unanswered/canceled call
             case 'calling': return 'calling';
             case 'incall': return 'in-call';
             case 'ACW': return 'acw';