Fix VPS replica clusters: barmanObjectStore serverName mismatch

CNPG's barmanObjectStore.serverName defaults to the externalClusters[]
entry's own .name field ('home-backup', an arbitrary label I chose) -
NOT the actual source Postgres cluster's name. Home's backup: block
(on the real pg-authentik/pg-n8n/pg-nextcloud Clusters) defaults
serverName to its own metadata.name instead. Without an explicit
override these two disagree, so recovery searches the object store
under the wrong server-name prefix and finds nothing - 'no target
backup found', confirmed live even after the ScheduledBackup fix
produced real, completed base backups.

infrastructure/vps-standby/n8n/manifests/cnpg-cluster.yaml

@@ -39,6 +39,10 @@ spec:
   externalClusters:
     - name: home-backup
       barmanObjectStore:
+        # See infrastructure/vps-standby/authentik/manifests/cnpg-cluster.yaml
+        # for why this override is required (serverName defaults to the
+        # externalClusters[].name, not the source cluster's real name).
+        serverName: pg-n8n
         destinationPath: s3://cnpg-backups/pg-n8n
         endpointURL: http://vps-minio.minio.svc.cluster.local:9000
         s3Credentials: