Add VPS warm-standby/backup site (Phase 0-1b)

Foundation for a DR/backup path using an always-on VPS as a second
ArgoCD-managed cluster, plus DB/backup standardization work that fell
out of it:

- vps-standby ArgoCD cluster destination + AppProject, MinIO backup
  receiver, VPS bootstrap script (k3s, Netbird, cert-manager)
- Dual-site DNS failover watcher + home-IP DDNS CronJob, Cloudflare
  token moved out of git into Vault+ExternalSecret
- Nextcloud migrated from ad-hoc MariaDB to CNPG + redis-operator
  (matches n8n/Authentik/GitLab's backup-native pattern)
- Authentik's CNPG manifests moved into the actual ArgoCD-synced
  manifests/ path (were present but never wired into the sync path)
- Vault raft-snapshot CronJob, CNPG barmanObjectStore backups
  (Authentik/n8n/Nextcloud), Nextcloud file-PVC restic sync - all
  targeting the new VPS MinIO receiver

See VPS Warm-Standby plan doc for full design rationale.

infrastructure/authentik/manifests/cnpg-podmonitor.yaml

@@ -0,0 +1,16 @@
+---
+apiVersion: monitoring.coreos.com/v1
+kind: PodMonitor
+metadata:
+  name: cnpg-postgres
+  namespace: authentik
+  labels:
+    release: prometheus
+spec:
+  selector:
+    matchLabels:
+      cnpg.io/cluster: pg-authentik
+  podMetricsEndpoints:
+    - port: metrics
+      path: /metrics
+      interval: 30s