docs(architecture): pivot to NAS genesis bootstrap

[jmgilman]

Summary

• make the N5 Pro NAS the IncusOS genesis node
• replace the UM760/VyOS bootstrap-k0s strategic baseline with a disposable Talos bootstrap cluster inside Incus
• update hardware, host, bootstrap, state/recovery, and Keycloak backup docs

Testing

• moon run docs:check --summary minimal
• git diff --check
• rg stale strategic references; remaining hits are explicit historical/non-goal references