refactor(frontend): Reactivityで型を明示するように (#12791)

* refactor(frontend): Reactivityで型を明示するように

* fix: プロパティの参照が誤っているのを修正

* fix: 初期化の値を空配列に書き換えていた部分をnullに置き換え

packages/frontend/src/pages/admin/overview.instances.vue

@@ -18,12 +18,13 @@ SPDX-License-Identifier: AGPL-3.0-only
 
 <script lang="ts" setup>
 import { ref } from 'vue';
+import * as Misskey from 'misskey-js';
 import * as os from '@/os.js';
 import { useInterval } from '@/scripts/use-interval.js';
 import MkInstanceCardMini from '@/components/MkInstanceCardMini.vue';
 import { defaultStore } from '@/store.js';
 
-const instances = ref([]);
+const instances = ref<Misskey.entities.FederationInstance[]>([]);
 const fetching = ref(true);
 
 const fetch = async () => {