Backups taken on a standby can silently never reach tier2

A backup taken on a standby instance can complete successfully (CNPG Backup reports completed, no error) while never being relayed to tier2. kopia snapshot list --all against the tier2 repository shows nothing for the affected cluster. There is no error, warning, or metric indicating the relay was skipped.

Starting a backup preferring the standby (which is the default) on the tier2 cluster and server samples is enough to reproduce the issue, for example using the cnpg plugin:

```
kubectl cnpg backup cluster-example -m plugin --plugin-name klio.cnpg.io
```

Reproduce the issue with `kubectl cnpg backup cluster-example -m plugin --plugin-name klio.cnpg.io`, then inspect the backup relay path for standby-preferred backups. Verify the affected cluster's repository with `kopia snapshot list --all`; done means the backup reaches tier2 or the skipped relay produces an error, warning, or metric.

Written by the indexing model from the issue text.