Add the first-shift tutorial design and state machine

Write the eight-beat tutorial sheet, its safe visitor script, persistence and
replay rules. Add a deterministic, skippable/restartable Tutorial RefCounted
state machine with headless tests. UI/GameManager wiring remains the next task.
Headless 235/235, Python 94/94.

src/game/tutorial.gd

@@ -0,0 +1,118 @@
+class_name Tutorial
+extends RefCounted
+## Deterministic first-shift tutorial state machine. It observes player actions
+## but owns no UI or simulation nodes, so it can be tested headlessly and wired
+## into GameManager without changing the shift FSM. `advance()` only accepts the
+## event for the current beat; wrong actions are ignored.
+
+signal beat_changed(index: int, beat: Dictionary)
+signal completed(skipped: bool)
+
+const BEATS := [
+	{
+		"id": "arrive",
+		"prompt": "Walk forward and look around. The entrance is behind you.",
+		"event": "moved",
+	},
+	{
+		"id": "focus",
+		"prompt": "Look at the visitor. Press Tab or the mouse wheel to cycle targets.",
+		"event": "cycled",
+	},
+	{
+		"id": "wheel",
+		"prompt": "Open the action wheel with Space or left click.",
+		"event": "wheel_opened",
+	},
+	{
+		"id": "inspect",
+		"prompt": "Choose Inspect and read the access evidence.",
+		"event": "inspected",
+	},
+	{
+		"id": "direction",
+		"prompt": "Close the panel and give a polite direction.",
+		"event": "polite_direction",
+	},
+	{
+		"id": "warning",
+		"prompt": "Give a formal warning if the visitor persists. It arms the body camera.",
+		"event": "formal_warning",
+		"alternate_event": "body_camera",
+	},
+	{
+		"id": "radio",
+		"prompt": "Open the assistance radio and submit a short report.",
+		"event": "radio_submitted",
+	},
+	{
+		"id": "review",
+		"prompt": "Finish the shift and review what happened.",
+		"event": "review_opened",
+	},
+]
+
+var index := -1
+var complete := false
+var skipped := false
+
+func start() -> Dictionary:
+	index = 0
+	complete = false
+	skipped = false
+	var beat: Dictionary = BEATS[0]
+	beat_changed.emit(index, beat)
+	return beat
+
+func current() -> Dictionary:
+	if index < 0 or index >= BEATS.size() or complete:
+		return {}
+	return BEATS[index]
+
+func prompt() -> String:
+	return str(current().get("prompt", ""))
+
+func advance(event: String) -> bool:
+	if complete:
+		return false
+	if index < 0:
+		start()
+	if index >= BEATS.size():
+		return false
+	var beat: Dictionary = BEATS[index]
+	var accepted: Array = [str(beat.get("event", ""))]
+	if beat.has("alternate_event"):
+		accepted.append(str(beat["alternate_event"]))
+	if event not in accepted:
+		return false
+	index += 1
+	if index >= BEATS.size():
+		complete = true
+		index = BEATS.size()
+		completed.emit(false)
+	else:
+		beat_changed.emit(index, BEATS[index])
+	return true
+
+## Skip is recorded separately so Settings/Help can offer "Replay tutorial".
+func skip() -> void:
+	if complete:
+		return
+	skipped = true
+	complete = true
+	index = BEATS.size()
+	completed.emit(true)
+
+func restart() -> Dictionary:
+	return start()
+
+func is_complete() -> bool:
+	return complete
+
+func is_skipped() -> bool:
+	return skipped
+
+## (current beat number, total beats); one-based for display, (total, total)
+## after completion.
+func progress() -> Vector2i:
+	return Vector2i(clampi(index + 1, 1, BEATS.size()), BEATS.size())