feat(CUB-58): Agent Status SignalR Service (Angular)

- Scaffold Angular 17 frontend with standalone components
- Add @microsoft/signalr package dependency
- Create AgentStatusService connecting to /hub endpoint
  - Auto-reconnect with progressive delays
  - Listens for AgentStatusChanged and BroadcastMessage
  - Logs all updates to console
  - Exposes statusUpdates$ and connected$ observables
  - onStatusUpdate() alias matching CUB-58 spec
- Create AgentStatusUpdate interface (agentId, status, lastSeenAt)
- Add APP_INITIALIZER provider to start connection on app boot
- Register initializer in app.config.ts
- Update .gitignore for frontend build artifacts

.gitignore

@@ -2,4 +2,10 @@ bin/
 obj/
 *.user
 *.suo
-.vs/
+.vs/
+
+# Frontend (Angular)
+frontend/node_modules/
+frontend/dist/
+frontend/.angular/
+frontend/*.log