feat: add MVP prompt and auth improvements

[luisfponce]

Summary

• add MVP prompt model/category option support and frontend prompt UX improvements
• harden signup so public registration always creates default user accounts
• add trusted god-user bootstrap CLI with database connection fallback and documentation
• update deployment configuration and backend/frontend validation coverage

Validation

• npm run build
• DB_URL=sqlite:///./test_auth_bootstrap.db pytest tests/functional/test_auth_routes.py tests/functional/test_admin_cli.py

Notes

• .kilo/ planning files remain untracked and are not included in this PR.