refactor(frontend): scripts -> utility

packages/frontend/src/utility/is-device-darkmode.ts

@@ -0,0 +1,8 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+export function isDeviceDarkmode() {
+	return window.matchMedia('(prefers-color-scheme: dark)').matches;
+}