#836 postgres max_connections=80 saturates: FATAL too many clients during test runs

EARS SPEC: - The postgres max_connections value shall exceed worst-case pool demand with headroom: api engine pool 2-64 + auth SQLAlchemy engine 5+5 overflow PER PROCESS (api + 5 workers = up to 60 for auth alone) + migrations/CLI/psql clients. - If connection slots are exhausted, then even superuser access fails because all services connect as user postgres (reserved slots consumed) - services shall use a non-superuser role (sub-task). Evidence: uncommitted compose tuning dropped max_connections 500->80 (applied on 2026-07-30 23:35 restart); full saturation at 2026-07-31 00:15 (psql FATAL); post-worker-restart steady state 37/80. Recommend max_connections=200 OR shrink pools (api 64 max is oversized for dev). Decision is the operator's - tuning change is theirs, uncommitted.