feat(enterprise): add backup and restore operations

[xe-nvdk]

Context

Enterprise backup workflows should be observable and operable from the same place as other Arc administration.

Scope

• Create, list, inspect, and delete backups
• Track backup progress and final status
• Restore workflow with target and impact summary
• Surface actionable errors and partial completion

Acceptance criteria

• Restore and delete actions require explicit confirmation
• Long-running state survives page refresh
• Backup identifiers and targets are unambiguous
• Capability and permission states are handled consistently