feat: 搭建应用基础框架

包含应用入口、根组件、路由配置（含登录守卫）、主布局、全局样式、ECharts 插件、类型定义、常量映射表及静态资源。

frontend/src/main.ts

@@ -0,0 +1,25 @@
+import { createApp } from 'vue'
+import { createPinia } from 'pinia'
+import ElementPlus from 'element-plus'
+import zhCn from 'element-plus/es/locale/lang/zh-cn'
+import 'element-plus/dist/index.css'
+
+// Font Awesome 图标
+import '@/assets/font-awesome/css/font-awesome.min.css'
+
+// ECharts（按需引入）+ vue-echarts 组件
+import '@/plugins/echarts'
+import VChart from 'vue-echarts'
+
+import App from './App.vue'
+import router from './router'
+import './styles/index.scss'
+
+const app = createApp(App)
+
+app.use(createPinia())
+app.use(router)
+app.use(ElementPlus, { locale: zhCn })
+app.component('VChart', VChart)
+
+app.mount('#app')