Mermaid diagrams up front, GFM alert callouts for key decisions and
gotchas, tables instead of bullet walls - replaces plain prose with
the visual template established for security-monitoring.md.
Secrets & PKI, Secret Distribution Model, SSO & Identity,
Firewall & Network Segmentation, DNS Naming Model, and Security
Monitoring - the first batch of per-system write-ups linked from
the new README, sourced and sanitized from the internal KB.