This change fixes backup-age alert notifications to display VM/CT names
instead of just "VMID XXX" in multi-cluster environments where backups
are stored on PBS.
Changes:
- Store all guests per VMID (not just first match) to handle VMID collisions across clusters
- Persist last-known guest names/types in metadata store for deleted VMs
- Enrich backup correlation with persisted metadata when live inventory is empty
- Update CheckBackups to handle multiple VMID matches intelligently
The fix addresses two scenarios:
1. Multiple PVE clusters with same VMID backing up to one PBS
2. VMs deleted from Proxmox but backups still exist on PBS
Backup-age alerts will now show proper VM/CT names when:
- A unique guest exists with that VMID (live or persisted)
- Multiple guests share a VMID (uses first match, consistent with current behavior)
When truly ambiguous (multiple live VMs, same VMID, no way to determine origin),
the alert gracefully falls back to showing "VMID XXX".
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