Adds src/services/bus (the only listen/emit site: one handler per contract
event plus the frontend-internal test-all event) and the React
context/reducer app store. Migrates the five scattered subscriptions
(layout events, pending failures, proxy refresh, profile update/timer,
test-all), deletes the old glue (events.ts, use-listen, use-layout-events,
LoadingCacheProvider), moves run state into the store, and adds an
architecture gate script wired into CI. Behavior is unchanged; the
run-state query's poll/focus safety net is preserved by the store
provider.
