Minimal plug for a Bier instance's admin server (PostgREST admin server).
Served on its own Bandit listener bound to admin_server_port, kept separate
from the catch-all API router so the health paths never collide with table
names. Exposes:
GET /live—200whenever the process is up (pure liveness).GET /ready—200whenBier.Health.ready?/1holds, else503.
Every other request returns 404. The instance name is supplied via
init/1 (name:) so readiness resolves the right pool and schema cache.