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.

apps/nextcloud/manifests/cnpg-cluster.yaml

@@ -0,0 +1,68 @@
+apiVersion: postgresql.cnpg.io/v1
+kind: Cluster
+metadata:
+  name: pg-nextcloud
+  namespace: nextcloud
+spec:
+  imageName: ghcr.io/cloudnative-pg/postgresql:16
+  instances: 2
+
+  resources:
+    requests:
+      memory: "512Mi"
+      cpu: "50m"
+    limits:
+      memory: "2Gi"
+      cpu: "500m"
+
+  affinity:
+    topologyKey: kubernetes.io/hostname
+
+  storage:
+    size: 20Gi
+    storageClass: rook-ceph-block
+
+  primaryUpdateStrategy: unsupervised
+
+  postgresql:
+    parameters:
+      max_connections: "200"
+      shared_buffers: "512MB"
+      effective_cache_size: "1536MB"
+      maintenance_work_mem: "128MB"
+      checkpoint_completion_target: "0.9"
+      wal_buffers: "16MB"
+      default_statistics_target: "100"
+      random_page_cost: "1.1"
+      effective_io_concurrency: "200"
+      work_mem: "2621kB"
+      min_wal_size: "1GB"
+      max_wal_size: "4GB"
+
+  bootstrap:
+    initdb:
+      database: nextcloud
+      owner: nextcloud
+
+  # Backup to the VPS MinIO backup receiver. VPS_MINIO_ENDPOINT placeholder
+  # matches infrastructure/vault/manifests/raft-snapshot-cronjob.yaml - replace
+  # with the VPS's actual Netbird address once bootstrapped. This covers the
+  # DB only - file PVC content is separate, see nextcloud-pvc-sync-cronjob.yaml.
+  backup:
+    barmanObjectStore:
+      destinationPath: s3://cnpg-backups/pg-nextcloud
+      endpointURL: http://vps-minio.netbird.internal:30900
+      s3Credentials:
+        accessKeyId:
+          name: vps-minio-secret
+          key: accesskey
+        secretAccessKey:
+          name: vps-minio-secret
+          key: secretkey
+      wal:
+        compression: gzip
+        maxParallel: 2
+    retentionPolicy: "30d"
+
+  monitoring:
+    enablePodMonitor: true