Fix README architecture diagram and destination wording

- Rename the README diagram's "Destinations" group to "Peers and services".
- Draw internet control as Hub "ask only (query)" and admin app
  "control + tap to approve"; draw Paperclip as "slow job (approved)".
- Keep the .mmd source in step with the README diagram.
- State the admin app's scope in the system overview.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

docs/outline/01-system-overview.md

@@ -37,6 +37,9 @@ Nothing here is ownership. These are directions of talk.
 - dsh chat — per-person chat.
 - Console portal — web dashboard.
 
+The admin app is also the trusted door. It calls a high-consequence control
+service directly, not through the Hub.
+
 ## Peers and Destinations
 
 Every other project is a peer. Each has its own folder, repo, port, and