feat(frontend): supervisor presence indicator on agent call card

- useAgentState hook returns { state, supervisorPresence }
- SSE events: supervisor-whisper → "Supervisor coaching" (blue badge)
  supervisor-barge → "Supervisor on call" (brand badge)
  supervisor-left → badge disappears
- Listen mode is silent — no badge shown
- Updated call sites: sidebar.tsx, agent-status-toggle.tsx destructure

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

src/components/call-desk/agent-status-toggle.tsx

@@ -33,7 +33,7 @@ type AgentStatusToggleProps = {
 export const AgentStatusToggle = ({ isRegistered, connectionStatus }: AgentStatusToggleProps) => {
     const agentConfig = localStorage.getItem('helix_agent_config');
     const agentId = agentConfig ? JSON.parse(agentConfig).ozonetelAgentId : null;
-    const ozonetelState = useAgentState(agentId);
+    const { state: ozonetelState } = useAgentState(agentId);
 
     const [menuOpen, setMenuOpen] = useState(false);
     const [changing, setChanging] = useState(false);