fix(kube): Update postgres volume mount for PG18 compatibility

PostgreSQL 18 Docker images changed the data directory layout to use
major-version-specific subdirectories under /var/lib/postgresql.

Mount point must be /var/lib/postgresql (not /data) to allow the
container to manage the versioned subdirectory structure.

See: docker-library/postgres#1259

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: icook

kube/app/templates/postgres.yaml

@@ -40,7 +40,7 @@ spec:
           name: postgres
         volumeMounts:
         - name: postgres-data
-          mountPath: /var/lib/postgresql/data
+          mountPath: /var/lib/postgresql
         readinessProbe:
           exec:
             command: