fix(frontend): テーマプレビューが見れない問題を修正 (#14097)

* fix(frontend): テーマプレビューが見れない問題を修正

* fix: MkPreview.vue, preview.vue

packages/frontend/src/pages/preview.vue

@@ -0,0 +1,26 @@
+<!--
+SPDX-FileCopyrightText: syuilo and misskey-project
+SPDX-License-Identifier: AGPL-3.0-only
+-->
+
+<template>
+<div>
+	<MkSample/>
+</div>
+</template>
+
+<script lang="ts" setup>
+import { computed } from 'vue';
+import MkSample from '@/components/MkPreview.vue';
+import { i18n } from '@/i18n.js';
+import { definePageMetadata } from '@/scripts/page-metadata.js';
+
+const headerActions = computed(() => []);
+
+const headerTabs = computed(() => []);
+
+definePageMetadata(computed(() => ({
+	title: i18n.ts.preview,
+	icon: 'ti ti-eye',
+})));
+</script>