README: fix diagram caption to match what the simplified diagram actually shows

Caption claimed all dashed arrows were telemetry reporting, but two
of them ('proxies', 'auth') are traffic-routing relationships, not
telemetry - the old caption was written for the full 20-edge version
and never updated when the diagram got simplified.

README.md

@@ -77,7 +77,7 @@ This repo is a sanitized showcase of the systems behind that platform — the ac
 ## Architecture at a glance
 
 ![Architecture Overview](assets/architecture-overview.svg)
-Solid arrows are real dependencies; dotted arrows are asynchronous telemetry reporting, not a blocking dependency. Full breakdown of all 8 traffic laws (ingress, east-west, secrets, DNS, observability, notifications, CI/CD, management) with the actual trust-boundary reasoning: [docs/architecture-overview.md](docs/architecture-overview.md).
+Solid arrows are hard dependencies — the target has to be reachable for the source to function. Dashed arrows are secondary relationships (request routing like "proxies"/"auth", or async telemetry reporting) that don't block the source if the target's unavailable. Full breakdown of all 8 traffic laws (ingress, east-west, secrets, DNS, observability, notifications, CI/CD, management) with the actual trust-boundary reasoning: [docs/architecture-overview.md](docs/architecture-overview.md).
 
 ## Systems