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/vps-minio-secret.yaml

@@ -0,0 +1,27 @@
+---
+# VPS MinIO credentials for CNPG's barmanObjectStore backup target, and reused
+# by the Phase 1b PVC-content sync CronJob. Same Vault source as
+# infrastructure/vault/manifests/raft-snapshot-cronjob.yaml
+# (secret/vps-minio-credentials) - populated once, manually, after VPS bootstrap.
+apiVersion: external-secrets.io/v1
+kind: ExternalSecret
+metadata:
+  name: vps-minio-credentials
+  namespace: nextcloud
+spec:
+  refreshInterval: 1h
+  secretStoreRef:
+    kind: ClusterSecretStore
+    name: vault-backend
+  target:
+    name: vps-minio-secret
+    creationPolicy: Owner
+  data:
+    - secretKey: accesskey
+      remoteRef:
+        key: vps-minio-credentials
+        property: access-key
+    - secretKey: secretkey
+      remoteRef:
+        key: vps-minio-credentials
+        property: secret-key