Add auth pages and gate lobby behind JWT sessions

[jackandcarter]

Summary

• add JWT cookie-based authentication endpoints, database support, and middleware to verify users
• add dedicated login/registration pages plus client helpers that redirect to the protected /lobby after success
• require authentication for lobby APIs and frontend bootstrap so unauthenticated visitors hit the auth flow first

Testing

• PORT=8080 NODE_ENV=development LOG_LEVEL=info MYSQL_HOST=localhost MYSQL_USER=root MYSQL_PASSWORD=password MYSQL_DATABASE=adventurebot JWT_SECRET=devsecret npm run build

---

Codex Task