Ship the 0.8.0 first-hour and campaign milestone

Add the campaign shell, pause-safe checkpoint resume, post-shift campaign
continue, confirmed campaign reset, difficulty presets, searchable Help,
content-matrix validation, recovery events, contextual dialogue, policy/debrief
context and eligible-event previews. Extend persistence with atomic separate
files and add campaign/checkpoint/tutorial smokes. Headless 247/247, Python
94/94, tutorial/campaign/session/scenario smokes green.

src/core/campaign.gd

@@ -0,0 +1,64 @@
+class_name Campaign
+extends RefCounted
+## Small campaign/session progression model. Venue rules stay in VenueScenario;
+## this only owns order, completed shifts, difficulty and the next venue.
+
+const ORDER := ["hollywood_building", "joke_shop", "tv_studio"]
+
+var index := 0
+var shift_number := 1
+var completed: Array[String] = []
+var difficulty := "normal"
+var complete := false
+var last_grade := ""
+
+func setup(data: Dictionary = {}) -> void:
+	index = clampi(int(data.get("index", 0)), 0, ORDER.size())
+	shift_number = maxi(1, int(data.get("shift_number", 1)))
+	difficulty = str(data.get("difficulty", "normal"))
+	completed.clear()
+	for item in data.get("completed", []):
+		var value := str(item)
+		if value in ORDER and value not in completed:
+			completed.append(value)
+	complete = bool(data.get("complete", index >= ORDER.size()))
+	last_grade = str(data.get("last_grade", ""))
+
+func next_venue() -> String:
+	if complete or index >= ORDER.size():
+		return ""
+	return ORDER[index]
+
+func summary() -> Dictionary:
+	return {
+		"index": index,
+		"next_venue": next_venue(),
+		"shift_number": shift_number,
+		"difficulty": difficulty,
+		"complete": complete,
+		"completed": completed.duplicate(),
+		"last_grade": last_grade,
+	}
+
+## Record one finished shift. Idempotent per venue for a single campaign run.
+func record_shift(scenario_id: String, review: Dictionary = {}) -> bool:
+	if complete:
+		return false
+	if scenario_id != next_venue():
+		return false
+	if scenario_id not in completed:
+		completed.append(scenario_id)
+	var rep: Dictionary = review.get("reputation", {})
+	last_grade = str(rep.get("grade", last_grade))
+	index += 1
+	shift_number = index + 1
+	if index >= ORDER.size():
+		complete = true
+	return true
+
+func set_difficulty(value: String) -> void:
+	if value in ["easy", "normal", "hard"]:
+		difficulty = value
+
+func reset() -> void:
+	setup({})