make demo-ui now starts the userservice (own Postgres + migrations) beside the
coordinator on a shared JWT secret, and seeds a root admin. The coordinator runs
in UI session mode, so /ui opens a login page instead of a basic-auth prompt.
- docker-compose.users.yml overlay: userservice stack + coordinator JWT wiring
- demo-ui.sh: waits for the userservice, logs in as the seeded admin to poll the
now session-gated dashboard, and prints the admin credentials
- validated with docker compose config (6 services, merged env)
