fix: mount postgres volume at new PGDATA path for postgres:18

The official postgres:18 image moved PGDATA from /var/lib/postgresql/data
to /var/lib/postgresql. Mounting the volume at the old path made the
entrypoint abort and the postgresql container restart-loop, failing the
deploy with "dependency postgresql failed to start". Mounting the volume
at /var/lib/postgresql fixes the deploy; server responds 200 on
/if/flow/initial-setup/.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

blueprints/authentik/docker-compose.yml

@@ -10,7 +10,7 @@ services:
       retries: 5
       timeout: 5s
     volumes:
-      - database:/var/lib/postgresql/data
+      - database:/var/lib/postgresql
     environment:
       POSTGRES_PASSWORD: ${PG_PASS}
       POSTGRES_USER: ${PG_USER}