fix(postgres): remove memory limit and add document database (#259)

## Summary

- Remove the 600Mi memory limit on the local Postgres Deployment. With `shared_buffers=384MB` + `max_connections=300` the pod was being repeatedly OOMKilled under real workloads, leaving clients with intermittent `connect: connection refused`. Keep the 400Mi request for scheduling.
- Add `document` to the seeded database list in `initdb.sh`.

## Test plan

- [x] `kubectl --context kind-unbound apply -f k8s/infra/postgres.yaml` — rollout succeeds
- [x] Postgres pod stable (0 restarts) after apply
- [ ] On a fresh cluster (`./setup`), verify the `document` database is created (requires empty `data/postgres/`)

Reviewed-on: #259

k8s/infra/postgres.yaml

@@ -23,6 +23,7 @@ data:
     	CREATE DATABASE authz WITH OWNER postgres ENCODING utf8;
     	CREATE DATABASE company WITH OWNER postgres ENCODING utf8;
     	CREATE DATABASE consumer WITH OWNER postgres ENCODING utf8;
+    	CREATE DATABASE document WITH OWNER postgres ENCODING utf8;
     	CREATE DATABASE employee WITH OWNER postgres ENCODING utf8;
     	CREATE DATABASE invoice WITH OWNER postgres ENCODING utf8;
     	CREATE DATABASE notification WITH OWNER postgres ENCODING utf8;
@@ -62,8 +63,6 @@ spec:
         resources:
           requests:
             memory: 400Mi
-          limits:
-            memory: 600Mi
         ports:
         - containerPort: 5432
         env: