feat: offline mode; PWA

src/components/App/UpdatePrompt.vue

@@ -0,0 +1,24 @@
+<template>
+  <div class="fixed z-50 bottom-0 right-0">
+    <button @click="onUpdateClick" class="p-3 m-3 bg-cyan-600 rounded-md text-xl" ref="updateBtnEl">
+      <div>{{ $t('update-prompt.line1') }}</div>
+      <u>{{ $t('update-prompt.line2') }}</u>
+    </button>
+  </div>
+</template>
+
+<script setup lang="ts">
+import { onMounted } from 'vue';
+import { ref } from 'vue';
+
+const emit = defineEmits(['onUpdateClick']);
+const updateBtnEl = ref<HTMLElement | null>(null);
+
+function onUpdateClick() {
+  emit('onUpdateClick');
+}
+
+onMounted(() => {
+  updateBtnEl.value?.focus();
+});
+</script>