feat: P4.6 agent demo + escalate button + support seed/smoke (P4 complete)

apps/agent-demo (Vite): agent sets AVAILABLE, sees assigned tickets, opens the
thread, replies. message-demo customer pane gains 'escalate to support' (via
SupportProvider/useEscalate). seed-support + smoke-support prove the loop:
escalate -> auto-assign -> agent reply -> customer receives. 45 tests; realtime/
inbox/support smokes all pass; both demos build.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/agent-demo/src/main.tsx

@@ -0,0 +1,5 @@
+import { createRoot } from 'react-dom/client';
+import { App } from './App';
+
+const el = document.getElementById('root');
+if (el) createRoot(el).render(<App />);