重新设计diff功能：使用Monaco Editor实现专业级文件对比

新增功能：
- DiffViewer组件：基于Monaco Editor DiffEditor的专业代码对比
- DiffWindow组件：专用的diff对比窗口包装器
- 并排/内联视图切换功能
- 多语言语法高亮支持
- 智能文件类型检测
- 完整的工具栏（下载、刷新、视图切换、行号切换）

技术改进：
- 替代原来的两个独立文件窗口方案
- 使用Monaco Editor提供VS Code同级的对比体验
- 支持大文件错误处理和SSH连接自动重连
- 专业的差异高亮显示（新增/删除/修改）

依赖更新：
- 新增@monaco-editor/react依赖

src/ui/Desktop/Apps/File Manager/components/DiffWindow.tsx

@@ -0,0 +1,75 @@
+import React from 'react';
+import { DraggableWindow } from './DraggableWindow';
+import { DiffViewer } from './DiffViewer';
+import { useWindowManager } from './WindowManager';
+import type { FileItem, SSHHost } from '../../../../types/index.js';
+
+interface DiffWindowProps {
+  windowId: string;
+  file1: FileItem;
+  file2: FileItem;
+  sshSessionId: string;
+  sshHost: SSHHost;
+  initialX?: number;
+  initialY?: number;
+}
+
+export function DiffWindow({
+  windowId,
+  file1,
+  file2,
+  sshSessionId,
+  sshHost,
+  initialX = 150,
+  initialY = 100
+}: DiffWindowProps) {
+  const { closeWindow, minimizeWindow, maximizeWindow, focusWindow, windows } = useWindowManager();
+
+  const currentWindow = windows.find(w => w.id === windowId);
+
+  // 窗口操作处理
+  const handleClose = () => {
+    closeWindow(windowId);
+  };
+
+  const handleMinimize = () => {
+    minimizeWindow(windowId);
+  };
+
+  const handleMaximize = () => {
+    maximizeWindow(windowId);
+  };
+
+  const handleFocus = () => {
+    focusWindow(windowId);
+  };
+
+  if (!currentWindow) {
+    return null;
+  }
+
+  return (
+    <DraggableWindow
+      title={`文件对比: ${file1.name} ↔ ${file2.name}`}
+      initialX={initialX}
+      initialY={initialY}
+      initialWidth={1200}
+      initialHeight={700}
+      minWidth={800}
+      minHeight={500}
+      onClose={handleClose}
+      onMinimize={handleMinimize}
+      onMaximize={handleMaximize}
+      onFocus={handleFocus}
+      isMaximized={currentWindow.isMaximized}
+      zIndex={currentWindow.zIndex}
+    >
+      <DiffViewer
+        file1={file1}
+        file2={file2}
+        sshSessionId={sshSessionId}
+        sshHost={sshHost}
+      />
+    </DraggableWindow>
+  );
+}