Implement prototype: venue-driven simulation core, scenarios, tests, and playable entrance scene

- Godot 4.3 project scaffold with first-person guard, procedural world,
  interaction HUD, access inspection, radio forms, debug overlay, shift review
- Simulation core: ShiftCoordinator, VenueScenario, EventScheduler, NPCController/FSM,
  AccessVerifier, EscalationManager, RadioSystem, IncidentRecorder,
  ReputationEvaluator, CrowdSystem, EventBus
- Three authored scenarios (Hollywood Blvd building, The Joke Shop, TV studio)
- Custom headless test runner (25 tests) replacing editor-dependent GUT,
  plus GitHub Actions CI
- Documentation workflow live: README, PLAN (tech stack), TODO/DONE, MEMORY

src/core/event_bus.gd

@@ -0,0 +1,17 @@
+class_name EventBus
+extends RefCounted
+## Instance-based event bus (ADR-0005 spirit). Owned by ShiftCoordinator and
+## passed to subsystems that need to notify observers. Subsystems emit only if
+## a bus is assigned, so headless tests never depend on global state.
+
+signal incident_recorded(incident: Dictionary)
+signal player_action(action: Dictionary)
+signal escalation_changed(payload: Dictionary)
+signal radio_call(call: Dictionary)
+signal responder_arrived(responder: Dictionary)
+signal npc_state_changed(payload: Dictionary)
+signal shift_state_changed(payload: Dictionary)
+signal reputation_changed(payload: Dictionary)
+signal crowd_changed(payload: Dictionary)
+signal access_decided(payload: Dictionary)
+signal shift_review_ready(review: Dictionary)