feat(mobile): register vant, MobileLayout, device-based routing, viewport meta

frontend/src/main.ts

@@ -3,7 +3,10 @@ import { createApp } from 'vue'
 import { createPinia } from 'pinia'
 import ElementPlus from 'element-plus'
 import 'element-plus/dist/index.css'
+import Vant from 'vant'
+import 'vant/lib/index.css'
 import './assets/design.css'
+import './assets/mobile.css'
 import * as ElementPlusIconsVue from '@element-plus/icons-vue'
 import App from './App.vue'
 import router from './router'
@@ -19,5 +22,6 @@ for (const [key, component] of Object.entries(ElementPlusIconsVue)) {
 app.use(pinia)
 app.use(router)
 app.use(ElementPlus)
+app.use(Vant)
 
 app.mount('#app')