[codex] Build enterprise AI support agent

[chengganguo]

Summary

• Convert the demo into an enterprise support AI agent with backend domain modules, persistence, evaluation scripts, and tests.
• Add customer portal and admin console flows, including shared /admin/login routing and admin workspace pages.
• Add production deployment examples, runbooks, monitoring config, and phase requirement/status docs.

Testing

• python-backend: pytest (63 passed, 1 skipped)
• ui: npm run build
• smoke: /admin/login?return_to=/admin/workspace returns 200; /login redirects to /admin/login; /admin/workspace returns 200