feat(meta): 商店池按 unlock_cost/已解锁门控（_available_pool）

scripts/autoloads/shop_manager.gd

@@ -30,11 +30,17 @@ func open_shop(seed_override: int = -1) -> void:
 	_refresh_slots()
 	EventBus.emit(EventID.SHOP_OPENED, {"seed": _shop_seed})
 
-func _refresh_slots() -> void:
-	# 纯数据驱动池：SpellRegistry（data/spells.json）中可购买（shop_cost>0）的法术
-	var pool: Array = SpellRegistry.get_all_ids().filter(func(id):
+## 商店可抽池：shop_cost>0 且（未门控 unlock_cost==0 或 已解锁）
+func _available_pool() -> Array:
+	return SpellRegistry.get_all_ids().filter(func(id):
 		var s: SpellNode = SpellRegistry.get_spell(id)
-		return s != null and int(s.meta.get("shop_cost", 0)) > 0)
+		if s == null or int(s.meta.get("shop_cost", 0)) <= 0:
+			return false
+		var uc: int = int(s.meta.get("unlock_cost", 0))
+		return uc == 0 or MetaProgress.is_unlocked(id))
+
+func _refresh_slots() -> void:
+	var pool: Array = _available_pool()
 	current_slots.clear()
 	for _i in SLOT_COUNT:
 		if pool.is_empty():