feat(stalwart): deploy Stalwart mail server with CNPG and S3

- stalwart namespace with Deployment + HPA (2-6 replicas)
- CNPG PostgreSQL cluster (3 instances, 20Gi cephrbd-fast-delete) with PgBouncer pooler
- S3/Ceph-RGW for blob storage (stalwart-maildata bucket, lz4 compressed)
- Secrets from Vault: postgres-credentials, s3-credentials, stalwart-admin
- TLS cert via cert-manager (vault-issuer) for mail.main.unkin.net
- SMTP relay on port 25 (internal ClusterIP, trusted pod CIDRs)
- Submission on port 587, IMAP 143/993, HTTPS 443 via LoadBalancer
- HTTP port 8080 for Traefik reverse proxy (web admin at mail.k8s.syd1.au.unkin.net)
- Outbound mail routed through postfix.mailgateway.svc.cluster.local:25
- Spam filtering offloaded to postfix/rspamd (disabled internally)

apps/base/stalwart/kustomization.yaml

@@ -0,0 +1,23 @@
+---
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+
+resources:
+  - certificate.yaml
+  - cnpg_cluster.yaml
+  - cnpg_pooler.yaml
+  - gateway.yaml
+  - httproute.yaml
+  - namespace.yaml
+  - services.yaml
+  - stalwart-deployment.yaml
+  - stalwart-hpa.yaml
+  - vaultauth.yaml
+  - vaultstaticsecret.yaml
+
+configMapGenerator:
+  - name: stalwart-config
+    files:
+      - config.toml=resources/config.toml
+    options:
+      disableNameSuffixHash: true