优化文件管理器视觉设计和安全性

核心改进：
- 统一图标色调：所有文件类型图标改为黑白配色，消除彩色差异
- 恢复原始主题：修复shadcn样式导致的过暗背景问题
- 增强大文件安全：后端10MB文件大小限制，防止内存溢出
- 优化警告样式：Large File Warning使用shadcn设计规范

技术细节：
- getFileIcon()全部使用text-muted-foreground统一色调
- 恢复bg-dark-bg/border-dark-border原始主题色彩
- readFile API增加stat文件大小检查和错误处理
- FileViewer警告组件使用destructive色彩体系

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

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

@@ -579,17 +579,17 @@ export function FileViewer({
         {/* 大文件警告对话框 */}
         {showLargeFileWarning && (
           <div className="h-full flex items-center justify-center bg-background">
-            <div className="bg-card border border-orange-200 rounded-lg p-6 max-w-md mx-4 shadow-lg">
+            <div className="bg-card border border-destructive/30 rounded-lg p-6 max-w-md mx-4 shadow-lg">
               <div className="flex items-start gap-3 mb-4">
-                <AlertCircle className="w-6 h-6 text-orange-500 flex-shrink-0 mt-0.5" />
+                <AlertCircle className="w-6 h-6 text-destructive flex-shrink-0 mt-0.5" />
                 <div>
                   <h3 className="font-medium text-foreground mb-2">Large File Warning</h3>
                   <p className="text-sm text-muted-foreground mb-3">
                     This file is {formatFileSize(file.size)} in size, which may cause performance issues when opened as text.
                   </p>
                   {isTooLarge ? (
-                    <div className="bg-red-50 border border-red-200 rounded p-3 mb-4">
-                      <p className="text-sm text-red-700 font-medium">
+                    <div className="bg-destructive/10 border border-destructive/30 rounded p-3 mb-4">
+                      <p className="text-sm text-destructive font-medium">
                         File is too large (&gt; 10MB) and cannot be opened as text for security reasons.
                       </p>
                     </div>

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

@@ -126,11 +126,17 @@ export function FileWindow({
       } catch (error: any) {
         console.error('Failed to load file:', error);
 
-        // 如果是连接错误，提供更明确的错误信息
-        if (error.message?.includes('connection') || error.message?.includes('established')) {
+        // 检查是否是大文件错误
+        const errorData = error?.response?.data;
+        if (errorData?.tooLarge) {
+          toast.error(`File too large: ${errorData.error}`, {
+            duration: 10000, // 10 seconds for important message
+          });
+        } else if (error.message?.includes('connection') || error.message?.includes('established')) {
+          // 如果是连接错误，提供更明确的错误信息
           toast.error(`SSH connection failed. Please check your connection to ${sshHost.name} (${sshHost.ip}:${sshHost.port})`);
         } else {
-          toast.error(`Failed to load file: ${error.message || 'Unknown error'}`);
+          toast.error(`Failed to load file: ${error.message || errorData?.error || 'Unknown error'}`);
         }
       } finally {
         setIsLoading(false);