Move backup resources from separate 'backup' namespace to 'forgejo':
- Change CronJob namespace from 'backup' to 'forgejo'
- Reuse existing forgejo-postgres-secret instead of duplicate backup secret
- Remove backup-namespace.yaml (no longer needed)
- Remove forgejo-backup-secret-sealed.yaml (using existing secret)
This simplifies the architecture by keeping all Forgejo-related
resources in a single namespace and eliminating credential duplication.
Co-Authored-By: Paperclip <noreply@paperclip.ing>
