Set default resource requests and limits so HPA can scale on CPU

What does this MR do?

Sets default resources requests/limits in values.yaml. Previously resources: {} meant no CPU request, so the HPA (80% CPU target) could not compute utilization and autoscaling was non-functional.

Defaults follow the smallest tier of the Secrets Manager sizing recommendations: CPU request 500m (limit 2x), memory request 2Gi with limit equal to request.

Closes #38