perf: 前端配置Element Plus按需引入，优化Axios错误拦截提示

frontend/src/main.ts

@@ -1,8 +1,8 @@
-import "element-plus/dist/index.css";
+import "element-plus/theme-chalk/el-message.css";
+import "element-plus/theme-chalk/el-message-box.css";
 import "vant/lib/index.css";
 import "./styles/base.css";
 
-import ElementPlus from "element-plus";
 import { createPinia } from "pinia";
 import { createApp } from "vue";
 
@@ -14,7 +14,7 @@ import { useSessionStore } from "./stores/session";
 const app = createApp(App);
 const pinia = createPinia();
 
-app.use(pinia).use(router).use(ElementPlus);
+app.use(pinia).use(router);
 
 window.addEventListener("auth-storage-changed", () => {
   useSessionStore(pinia).syncFromStorage();