Completes the docs/ set - all 16 systems now have a full deep-dive
page in the diagram+callout+table style. Architecture overview covers
the 4 trust boundaries and 2 traffic planes; IaC pipeline is a fresh
Packer->Terraform->Ansible writeup replacing the stale old-content/
snapshot; disaster recovery covers the 3 independent backup layers
and the deliberately decoupled OS/app upgrade systems.
