docs: update documentation to OKF v0.1 format

docs/api/system.md

@@ -114,7 +114,10 @@ Each frame:
 See `backend/src/common/services/event-status.service.ts` for the
 authoritative state machine; see
 [Event Window Guide](/guides/event-window.md) for the full diagram and
-the SPA wiring.
+the SPA wiring. The authenticated browser consumer uses the fetch-based
+transport in `frontend/src/app/core/services/authenticated-event-source.service.ts`
+so it can send the JWT `Authorization` header; native `EventSource` cannot set
+that header.
 
 # `GET /api/v1/event/stream` (public SSE, legacy)