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/radio_system.gd

@@ -0,0 +1,106 @@
+class_name RadioSystem
+extends RefCounted
+
+const Rules := preload("res://src/core/rules.gd")
+const EventBus := preload("res://src/core/event_bus.gd")
+## Radio call handling (PLAN.md: Level 4 radio assist, Level 5 emergency).
+## - Level 4: security assistance with a report form, arrival delay.
+## - Level 5: emergency radio, hold-to-confirm enforced by calling layer,
+##   cooldown and battery limits to prevent spam.
+## - Incorrect/exaggerated reports damage credibility (recorded via reporter).
+
+signal call_made(call_data: Dictionary)
+signal responder_arrived(call_data: Dictionary)
+
+var battery: float = 100.0
+var max_battery: float = 100.0
+var emergency_cooldown_remaining: float = 0.0
+var emergency_cooldown_seconds: float = 120.0
+var battery_cost_emergency: float = 30.0
+var battery_cost_assist: float = 10.0
+
+var accepting_calls := true
+var event_bus: EventBus = null
+
+func set_event_bus(bus: EventBus) -> void:
+	event_bus = bus
+
+## report: { npc_id, location, description, behavior, weapons_seen, danger_level: 0..3 }
+func request_assistance(report: Dictionary) -> Dictionary:
+	var result := {
+		"ok": false,
+		"level": Rules.Level.RADIO_ASSIST,
+		"reason": "",
+		"call": {},
+	}
+	if not accepting_calls:
+		result.reason = "Radio not accepting calls"
+		return result
+	if battery < battery_cost_assist:
+		result.reason = "battery depleted"
+		return result
+	battery -= battery_cost_assist
+	var call := {
+		"type": "assist",
+		"report": report.duplicate(),
+		"placed_at_ms": Time.get_ticks_msec(),
+		"arrival_delay_s": 8.0,
+		"responder": "security",
+	}
+	result.ok = true
+	result.call = call
+	call_made.emit(call)
+	if event_bus:
+		event_bus.radio_call.emit(call)
+	return result
+
+## Emergency call. The caller (UI) must handle hold-to-confirm; this applies
+## cooldown and battery limits.
+func request_emergency(report: Dictionary) -> Dictionary:
+	var result := {
+		"ok": false,
+		"level": Rules.Level.EMERGENCY,
+		"reason": "",
+		"call": {},
+	}
+	if not accepting_calls:
+		result.reason = "Radio not accepting calls"
+		return result
+	if emergency_cooldown_remaining > 0.0:
+		result.reason = "Cooldown active (%.1fs)" % emergency_cooldown_remaining
+		return result
+	if battery < battery_cost_emergency:
+		result.reason = "battery depleted"
+		return result
+	battery -= battery_cost_emergency
+	emergency_cooldown_remaining = emergency_cooldown_seconds
+	var call := {
+		"type": "emergency",
+		"report": report.duplicate(),
+		"placed_at_ms": Time.get_ticks_msec(),
+		"arrival_delay_s": 15.0,
+		"responder": "armed_responder",
+	}
+	result.ok = true
+	result.call = call
+	call_made.emit(call)
+	if event_bus:
+		event_bus.radio_call.emit(call)
+	return result
+
+## Report inaccuracies deserve a reputation hit. Caller uses this helper.
+static func credibility_hits(report: Dictionary, truth: Dictionary) -> int:
+	var hits := 0
+	if report.get("weapons_seen", false) != truth.get("weapons_seen", false):
+		hits += 1
+	var danger: int = report.get("danger_level", 0)
+	var actual_danger: int = truth.get("danger_level", 0)
+	if danger != actual_danger:
+		hits += 1
+	return hits
+
+## Advance cooldown; called by the simulation tick.
+func tick(delta: float) -> void:
+	if emergency_cooldown_remaining > 0.0:
+		emergency_cooldown_remaining = maxf(0.0, emergency_cooldown_remaining - delta)
+		# Battery could slowly recharge over a shift; keep it static for now.