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)

src/test/tests/test_audio_feedback.gd

@@ -0,0 +1,78 @@
+extends RefCounted
+## Audio feedback: a looping crowd bed that follows the crowd mood, and radio
+## crackle on open/close. All procedural, no audio assets, headless-safe.
+
+const AudioFeedback := preload("res://src/game/audio_feedback.gd")
+const CrowdSystem := preload("res://src/core/crowd_system.gd")
+
+func test_bed_volume_follows_mood() -> bool:
+	var quiet: float = AudioFeedback._level_to_db(0.0)
+	var loud: float = AudioFeedback._level_to_db(1.0)
+	var mid: float = AudioFeedback._level_to_db(0.5)
+	var a := TestUtils.check(quiet < -30.0, "a calm street keeps the bed quiet")
+	var b := TestUtils.check(loud > quiet, "panic raises the bed")
+	var c := TestUtils.check(mid > quiet and mid < loud, "the rise is gradual")
+	return a and b and c
+
+func test_crowd_level_is_clamped() -> bool:
+	var audio: Node = AudioFeedback.new()
+	audio.set_crowd_level(-1.0)
+	var a := TestUtils.check_eq(audio.crowd_level, 0.0, "negative mood clamps to 0")
+	audio.set_crowd_level(3.0)
+	var b := TestUtils.check_eq(audio.crowd_level, 1.0, "over-unity mood clamps to 1")
+	audio.free()
+	return a and b
+
+func test_crowd_stream_loops() -> bool:
+	var audio: Node = AudioFeedback.new()
+	var stream: AudioStreamWAV = audio._build_crowd_stream()
+	var a := TestUtils.check(stream != null, "a crowd stream is generated")
+	var b := TestUtils.check_eq(stream.loop_mode, AudioStreamWAV.LOOP_FORWARD, "the bed loops")
+	var c := TestUtils.check(stream.data.size() > 1000, "the bed has audio data")
+	var d := TestUtils.check(stream.data.size() == stream.loop_end * 2, "loop covers the whole buffer")
+	audio.free()
+	return a and b and c and d
+
+func test_crowd_bed_is_headless_safe() -> bool:
+	# No tree, no audio server: none of these may crash.
+	var audio: Node = AudioFeedback.new()
+	audio.start_crowd_bed()
+	var a := TestUtils.check(audio.bed_playing, "start marks the bed as playing")
+	audio.set_crowd_level(0.78)
+	var b := TestUtils.check(is_equal_approx(audio.crowd_level, 0.78), "level is stored")
+	audio.stop_crowd_bed()
+	var c := TestUtils.check(not audio.bed_playing, "stop clears the playing flag")
+	audio.free()
+	return a and b and c
+
+func test_radio_crackle_methods() -> bool:
+	var audio: Node = AudioFeedback.new()
+	audio.play_radio_open()
+	audio.play_radio_close()
+	var a := TestUtils.check_eq(audio.radio_crackles, 2, "open and close each count a crackle")
+	var b := TestUtils.check(audio._free_player() == null, "no players exist before _ready, and that is safe")
+	audio.free()
+	return a and b
+
+func test_game_manager_wires_audio() -> bool:
+	var src := FileAccess.get_file_as_string("res://src/game/game_manager.gd")
+	var a := TestUtils.check(src.contains("audio.start_crowd_bed()"), "the bed starts with the shift")
+	var b := TestUtils.check(src.contains("audio.set_crowd_level(float(payload.get("),
+		"crowd events drive the bed")
+	var c := TestUtils.check(src.contains("audio.stop_crowd_bed()"), "the bed stops at shift end")
+	var d := TestUtils.check(src.contains("audio.play_radio_open()"), "opening the radio crackles")
+	var e := TestUtils.check(src.contains("audio.play_radio_close()"), "closing the radio crackles")
+	return a and b and c and d and e
+
+func test_mood_events_reach_the_bed() -> bool:
+	## The bed level is fed from the same payload the crowd reactions use.
+	var crowd := CrowdSystem.new()
+	var seen: Array = []
+	crowd.changed.connect(func(_p): pass)
+	crowd.apply_event("aggressive_behavior")
+	seen.append(crowd.mood)
+	crowd.apply_event("emergency_responder")
+	seen.append(crowd.mood)
+	var a := TestUtils.check(seen[1] > seen[0], "mood rises with a responder arrival")
+	crowd = null
+	return a