Arx + Backsies modules in the Lanetti agent

Imported from GitHub issue El-SaMa/oma#155 by @El-SaMa.

• Arx malware/server/firewall module on the shared agent
• Backsies restic backups of app volumes (before every upgrade + scheduled)
• Managed VPS add-on bundle (Arx, security updates, monitoring, snapshots, support) ~+15-25 EUR/mo to verify

Design doc: https://claude.ai/code/artifact/8e38762a-5369-45d1-a64d-fce59d2e560b