arrstack: raise arrstack-postgres resources after OOMKills

Both replicas OOMKilled at the 1Gi limit on 2026-08-23, causing a
failover and a stuck replica. Raise requests to 1Gi/250m and limits
to 2Gi/1 cpu.

apps/base/arrstack/postgres/cnpg_cluster.yaml

@@ -147,10 +147,10 @@ spec:
   resources:
     limits:
       cpu: "1"
-      memory: 1Gi
+      memory: 2Gi
     requests:
-      cpu: 50m
+      cpu: 250m
-      memory: 512Mi
+      memory: 1Gi
   smartShutdownTimeout: 180
   startDelay: 3600
   stopDelay: 1800