fix(meta): 解锁面板 sid/scost 显式类型（get_all_ids 返回无类型 Array）

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

scenes/ui/main_menu.gd

@@ -419,8 +419,8 @@ func _rebuild_unlock() -> void:
 		else:
 			btn.text = tr("META_UNLOCK_BTN") % cost
 			btn.disabled = MetaProgress.aether < cost
-			var sid := id
-			var scost := cost
+			var sid: String = id
+			var scost: int = cost
 			btn.connect("pressed", func():
 				if MetaProgress.unlock(sid, scost):
 					AudioManager.play("buy")