升级Vue3，iView替换ElementPlus

- 删除babel配置、更新依赖与入口初始化
- 全量替换UI组件、样式适配，新增迁移文档与标签/过滤器自动化替换脚本

im/src/utils/message.js

@@ -0,0 +1,11 @@
+import { ElMessage, ElMessageBox, ElNotification } from "element-plus";
+
+export { ElNotification, ElMessage, ElMessageBox };
+
+export function setupLegacyMessage(app) {
+  app.config.globalProperties.$message = ElMessage;
+  app.config.globalProperties.$notify = ElNotification;
+  app.config.globalProperties.$confirm = ElMessageBox.confirm;
+  app.config.globalProperties.$prompt = ElMessageBox.prompt;
+  app.config.globalProperties.$alert = ElMessageBox.alert;
+}