refactor(frontend): migrate from Vite to Nuxt SPA

Replace Vite and Vue Router with Nuxt framework
Update Docker, build scripts, and env vars for Nuxt generate

frontend/pages/admin.vue

@@ -0,0 +1,13 @@
+<script setup lang="ts">
+import AdminView from '../src/views/AdminView.vue';
+
+definePageMeta({
+  name: 'admin',
+  requiredPermission: 'admin.access',
+  seo: { titleKey: 'pages.admin.title', descriptionKey: 'pages.admin.subtitle', noindex: true }
+});
+</script>
+
+<template>
+  <AdminView />
+</template>