plan-approve-once policy + cooler empty states + remove graph header

Backend:
- proposePlan sets plan window in autonomy_settings (nomos:plan:<session>)
- run handler checks plan window — auto-executes config_mutation commands
  within plan without per-action approval
- planWindowActive function in server.go
- Plan window cleaned up on completeTask (already covered by LIKE '%:' || )

Frontend:
- Removed 'Session graph' header bar
- Cooler empty states: Plan shows animated dots + 'Awaiting plan…',
  Activity shows pulsing dots + 'Waiting for activity…'

VERSION

@@ -1 +1 @@
-0.3.7
+0.3.8