feat: ✨ Add custom page if no connection available

frontend/src/App.vue

@@ -1,10 +1,27 @@
 <script setup>
+import { ref, onMounted, onBeforeUnmount } from 'vue'
 import { registerSW } from 'virtual:pwa-register'
 import { useAppStore } from './stores/app.js'
 import HeaderMain from './components/HeaderMain.vue'
 
 const appStore = useAppStore()
 
+const online = ref(navigator.onLine)
+
+const updateOnlineStatus = () => {
+  online.value = navigator.onLine
+}
+
+onMounted(() => {
+  window.addEventListener('online', updateOnlineStatus)
+  window.addEventListener('offline', updateOnlineStatus)
+})
+
+onBeforeUnmount(() => {
+  window.removeEventListener('online', updateOnlineStatus)
+  window.removeEventListener('offline', updateOnlineStatus)
+})
+
 registerSW({ immediate: true })
 
 </script>