Implement unified file editing for all non-media files

Major improvements:
- Remove separate view/edit modes - editing state can view content too
- Expand text editing support to ALL file types except media/binary files
- Add realistic undo functionality for copy/cut operations
- Implement moveSSHItem API for proper cross-directory file moves
- Add file existence checks to prevent copy failures
- Enhanced error logging with full command and path information

Key changes:
- FileWindow: Expand editable file types to exclude only media extensions
- FileViewer: Remove view mode toggle, direct editing interface
- Backend: Add moveItem API endpoint for cut operations
- Backend: Add file existence verification before copy operations
- Frontend: Complete undo system for copy (delete copied files) and cut (move back to original location)

File type handling:
- Media files (jpg, mp3, mp4, etc.) → Display only
- All other files → Direct text editing (js, py, txt, config files, unknown extensions)

🤖 Generated with Claude Code

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

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

@@ -436,6 +436,7 @@ export function FileViewer({
           </div>
 
           <div className="flex items-center gap-2">
+            {/* 编辑工具栏 - 直接显示，无需切换 */}
             {isEditable && (
               <>
                 <Button
@@ -705,7 +706,7 @@ export function FileViewer({
                         {renderHighlightedText(editedContent)}
                       </div>
                     ) : (
-                      // 没有搜索时显示可编辑的textarea
+                      // 直接显示可编辑的textarea
                       <textarea
                         value={editedContent}
                         onChange={(e) => handleContentChange(e.target.value)}
@@ -716,8 +717,9 @@ export function FileViewer({
                     )}
                   </div>
                 ) : (
+                  // 只有非可编辑文件（媒体文件）才显示为只读
                   <div className="h-full p-4 font-mono text-sm whitespace-pre-wrap overflow-auto bg-background text-foreground">
-                    {content ? renderHighlightedText(content) : 'File is empty'}
+                    {editedContent || content || 'File is empty'}
                   </div>
                 )}
               </div>