Add procedural crowd ambience and radio crackle

- AudioFeedback.start_crowd_bed() builds a 4 s looping AudioStreamWAV at runtime
  (one-pole filtered noise plus a 68/103 Hz drone, seeded) and set_crowd_level()
  maps crowd mood 0..1 to -34..-12 dB, so the street gets louder as it gets
  agitated or panics. The bed starts with the shift and stops at shift end.
- play_radio_open()/play_radio_close() push short filtered-noise bursts; wired to
  opening the radio panel, submitting a report, cancelling, and closing the panel.
- Still asset-free and headless-safe: with a dummy audio server the calls no-op.
  _free_player() returns null before _ready and callers handle it.

Tests/docs
- Headless suite 127 -> 134 (test_audio_feedback.gd).
- New smoke_audio.gd: bed playing, level follows mood events, radio crackles once
  per open/close, bed stops at shift end. Verified windowed (real audio server).
- README, TODO section moved to DONE, MEMORY. Version 0.2.8.

src/test/smoke_audio.gd

@@ -0,0 +1,85 @@
+extends SceneTree
+## Audio smoke: starts a shift, verifies the crowd bed is playing and follows mood
+## events, and that opening/closing the radio triggers crackle cues.
+##
+## Usage:
+##   godot --headless --path . --script res://src/test/smoke_audio.gd
+## (Headless uses a dummy audio server; the calls must still be safe.)
+
+const MAX_FRAMES := 900
+
+var frame := 0
+var gm: Node = null
+var started := false
+var step := 0
+var failures: Array[String] = []
+
+func _initialize() -> void:
+	root.size = Vector2i(1280, 720)
+	root.add_child(load("res://scenes/main.tscn").instantiate())
+
+func _process(_delta: float) -> bool:
+	frame += 1
+	if gm == null:
+		gm = root.find_child("GameManager", true, false)
+		return false
+	if not started:
+		gm.call("_on_venue_selected", "hollywood_building")
+		started = true
+		return false
+	if frame > MAX_FRAMES:
+		_fail("timeout")
+		return true
+	if frame < 120:
+		return false
+	match step:
+		0:
+			_check(gm.audio.bed_playing, "the crowd bed is playing during the shift")
+			var before: float = gm.audio.crowd_level
+			gm.coordinator.crowd.apply_event("aggressive_behavior")
+			_check(gm.audio.crowd_level > before, "an aggressive event raises the bed level")
+			gm.coordinator.crowd.apply_event("emergency_responder")
+			_check(gm.audio.crowd_level > before, "the responder keeps it up")
+			step = 1
+		1:
+			if gm.npcs.is_empty():
+				return false
+			gm.call("_on_guard_target", gm.npcs[0])
+			var crackles: int = gm.audio.radio_crackles
+			gm.call("_open_radio", false)
+			_check(gm.audio.radio_crackles == crackles + 1, "opening the radio crackles once")
+			gm.call("_on_radio_submitted", {
+				"npc_id": gm.current_incident_npc_id,
+				"location": "entrance",
+				"description": "tourist",
+				"behavior": "standing",
+				"weapons_seen": false,
+				"danger_level": 1,
+			}, false)
+			_check(gm.audio.radio_crackles == crackles + 2, "closing the radio crackles once")
+			gm.coordinator.call("_finish_shift")
+			_check(not gm.audio.bed_playing, "the bed stops when the shift ends")
+			step = 2
+		2:
+			_finish()
+			return true
+	return false
+
+func _check(condition: bool, message: String) -> void:
+	if condition:
+		print("ok: " + message)
+	else:
+		_fail(message)
+
+func _fail(message: String) -> void:
+	failures.append(message)
+	_finish()
+
+func _finish() -> void:
+	if failures.is_empty():
+		print("SMOKE OK: crowd bed and radio crackle")
+		quit(0)
+	else:
+		for message in failures:
+			printerr("SMOKE FAIL: " + message)
+		quit(1)