feat: real-time active call SSE — hold/unhold status for supervisor live monitor

- SupervisorService: added activeCallSubject (RxJS Subject), emits on all
  activeCalls Map mutations (Answered, Calling, Disconnect, Hold, Unhold)
- SupervisorController: new @Sse('active-calls/stream') endpoint
- OzonetelAgentController: callControl HOLD/UNHOLD updates activeCalls Map
  status via supervisor.updateCallStatus()

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

src/ozonetel/ozonetel-agent.controller.ts

@@ -382,6 +382,13 @@ export class OzonetelAgentController {
 
         try {
             const result = await this.ozonetelAgent.callControl(body);
+
+            if (body.action === 'HOLD') {
+                this.supervisor.updateCallStatus(body.ucid, 'on-hold');
+            } else if (body.action === 'UNHOLD') {
+                this.supervisor.updateCallStatus(body.ucid, 'active');
+            }
+
             return result;
         } catch (error: any) {
             const message = error.response?.data?.message ?? error.message ?? 'Call control failed';