fix(index): update welcome message to reflect Nuxt 4

app/pages/index/index.vue

@@ -4,7 +4,7 @@ const { user, isLoggedIn } = useAuth()
 
 <template>
     <div class="flex flex-col items-center justify-center min-h-screen">
-        <h1 class="text-4xl font-bold mb-4">Welcome to Nuxt 3!</h1>
+        <h1 class="text-4xl font-bold mb-4">Welcome to Nuxt 4!</h1>
         <p class="text-lg text-gray-600">This is the index page.</p>
         <p>{{ isLoggedIn }}</p>
         <p>{{ user }}</p>