FIX: Automatically cleanup deleted files from recent/pinned lists

File Cleanup Implementation:
- Detect file-not-found errors when opening files from recent/pinned lists
- Automatically remove missing files from both recent and pinned file lists
- Refresh sidebar to reflect updated lists immediately after cleanup
- Prevent error dialogs from appearing when files are successfully cleaned up

Backend Improvements:
- Enhanced SSH file manager to return proper 404 status for missing files
- Added fileNotFound flag in error responses for better error detection
- Improved error categorization for file access failures

Frontend Error Handling:
- Added onFileNotFound callback prop to FileWindow component
- Implemented handleFileNotFound function in FileManagerModern
- Enhanced error detection logic to catch various "file not found" scenarios
- Better error messages with internationalization support

Translation Additions:
- fileNotFoundAndRemoved: Notify user when file is cleaned up
- failedToLoadFile: Generic file loading error message
- serverErrorOccurred: Server error fallback message
- Chinese translations for all new error messages

Technical Details:
- Uses existing removeRecentFile and removePinnedFile API calls
- Triggers sidebar refresh via setSidebarRefreshTrigger
- Maintains backward compatibility with existing error handling
- Preserves error logging for debugging purposes

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

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

src/backend/ssh/file-manager.ts

@@ -622,9 +622,19 @@ app.get("/ssh/file_manager/ssh/readFile", (req, res) => {
               fileLogger.error(
                 `SSH readFile command failed with code ${code}: ${errorData.replace(/\n/g, " ").trim()}`,
               );
+
+              // Check if it's a "file not found" error
+              const isFileNotFound =
+                errorData.includes("No such file or directory") ||
+                errorData.includes("cannot access") ||
+                errorData.includes("not found");
+
               return res
-                .status(500)
-                .json({ error: `Command failed: ${errorData}` });
+                .status(isFileNotFound ? 404 : 500)
+                .json({
+                  error: `Command failed: ${errorData}`,
+                  fileNotFound: isFileNotFound
+                });
             }
 
             res.json({ content: data, path: filePath });