- Add notify_update_available() method to NotificationService
- Add translations for update notifications (ru/en)
- Add 'update' type to default notification types
- Add check_for_panel_updates() background task (runs every 6 hours)
- Notifications include link to settings page for easy update access
- Prevent duplicate notifications for same version
- Added IPAM release in sync_vm_cache when VM is no longer found on Proxmox
- Works when VMs deleted through Proxmox UI (not through panel)
- Logs released IPs count in sync summary
- Also includes server availability monitoring with notifications
