Allow the app package to import config

Why: The listen guard reads auth and host policy from config before the database opens, so app depending on config is a real edge.
Evidence: make test stopped in lint-boundaries on backend/app backend/config. The edge is now in the baseline.
Impact: New imports still fail the ratchet. This one records the startup guard's dependency.
Refs: .task/feature-sillytavern-review.md
Co-authored-by: Cursor <cursoragent@cursor.com>

policy/architecture-baseline.json

@@ -2,6 +2,7 @@
   "backend/app backend/bus",
   "backend/app backend/cardsvc",
   "backend/app backend/cmdbus",
+  "backend/app backend/config",
   "backend/app backend/hostapi",
   "backend/app backend/intentgate",
   "backend/app backend/pgbus",