新增: 文件操作增强与预览扩展

- 文件剪贴板复制剪切粘贴，重名自动副本
- SFTP下载到本机与外部文件拖入，目录递归
- 传输进度浮动面板，transfer-progress事件链
- Drawio预览，Excel工作线程，冻结看门狗
- cmd与bat自写batch语法高亮，psm1等映射补齐

frontend/src/plugin/built-in/drawio-handler.ts

@@ -0,0 +1,22 @@
+// drawio 预览插件注册
+// canHandle 严格匹配 .drawio / .dio 扩展名,不认 .xml(避免误吞配置文件,配置文件走代码编辑器)。
+
+import type { Component } from 'vue'
+import { registerPreviewHandler } from '../registry'
+import type { FilePreviewHandlerDefinition } from '../types'
+
+// 仅 .drawio / .dio;.drawio.png / .drawio.svg 本就走图片预览,不冲突
+const DRAWIO_EXT_REGEX = /\.(drawio|dio)$/i
+
+const drawioHandler: FilePreviewHandlerDefinition = {
+  id: 'drawio-preview',
+  name: 'Draw.io 查看器',
+  icon: '📊',
+  priority: 90,
+  canHandle: (filename: string): boolean => DRAWIO_EXT_REGEX.test(filename || ''),
+  getComponent: (): Promise<Component> =>
+    import('../../components/FileSystem/components/DrawioPreview.vue').then(m => m.default),
+  supportsEdit: false,
+}
+
+registerPreviewHandler(drawioHandler)