Preserve local paths for desktop saves (#5543)

# Summary

- Adds desktop file tracking: local paths are preserved and save buttons
now work as expcted (doing Save/Save As as appropriate)
- Adds logic to track whether files are 'dirty' (they've been modified
by some tool, and not saved to disk yet).
- Improves file state UX (dirty vs saved) and close warnings
- Web behaviour should be unaffected by these changes

## Indicators
Files now have indicators in desktop mode to tell you their state.

### File up-to-date with disk

<img width="318" height="393" alt="image"
src="https://github.com/user-attachments/assets/06325f9a-afd7-4c2f-8a5b-6d11e3093115"
/>

### File modified by a tool but not saved to disk yet

<img width="357" height="385" alt="image"
src="https://github.com/user-attachments/assets/1a7716d9-c6f7-4d13-be0d-c1de6493954b"
/>

### File not tracked on disk

<img width="312" height="379" alt="image"
src="https://github.com/user-attachments/assets/9cffe300-bd9a-4e19-97c7-9b98bebefacc"
/>

# Limitations
- It's a bit weird that we still have files stored in indexeddb in the
app, which are still loadable. We might want to change this behaviour in
the future
- Viewer's Save doesn't persist to disk. I've left that out here because
it'd need a lot of testing to make sure the logic's right with making
sure you can leave the Viewer with applying the changes to the PDF
_without_ saving to disk
- There's no current way to do Save As on a file that has already been
persisted to disk - it's only ever Save. Similarly, there's no way to
duplicate a file.

---------

Co-authored-by: James Brunton <[email protected]>
Co-authored-by: James Brunton <[email protected]>

frontend/src/core/utils/automationConverter.ts

@@ -4,6 +4,7 @@
 
 import { AutomationConfig } from '@app/types/automation';
 import { ToolRegistry } from '@app/data/toolsTaxonomy';
+import { downloadFile } from '@app/services/downloadService';
 import { ToolId } from '@app/types/toolId';
 
 /**
@@ -95,16 +96,5 @@ export function downloadFolderScanningConfig(
   const config = convertToFolderScanningConfig(automation, toolRegistry);
   const json = JSON.stringify(config, null, 2);
   const blob = new Blob([json], { type: 'application/json' });
-  const url = URL.createObjectURL(blob);
-
-  const a = document.createElement('a');
-  a.href = url;
-  a.download = `${automation.name}.json`;
-  a.style.display = 'none';
-
-  document.body.appendChild(a);
-  a.click();
-  document.body.removeChild(a);
-
-  URL.revokeObjectURL(url);
+  void downloadFile({ data: blob, filename: `${automation.name}.json` });
 }

frontend/src/core/utils/downloadUtils.ts

@@ -1,6 +1,7 @@
 import { StirlingFileStub } from '@app/types/fileContext';
 import { fileStorage } from '@app/services/fileStorage';
 import { zipFileService } from '@app/services/zipFileService';
+import { downloadFile } from '@app/services/downloadService';
 
 /**
  * Downloads a blob as a file using browser download API
@@ -8,17 +9,7 @@ import { zipFileService } from '@app/services/zipFileService';
  * @param filename - The filename for the download
  */
 export function downloadBlob(blob: Blob, filename: string): void {
-  const url = URL.createObjectURL(blob);
-
-  const link = document.createElement('a');
-  link.href = url;
-  link.download = filename;
-  document.body.appendChild(link);
-  link.click();
-  document.body.removeChild(link);
-
-  // Clean up the blob URL
-  URL.revokeObjectURL(url);
+  void downloadFile({ data: blob, filename });
 }
 
 /**
@@ -34,8 +25,11 @@ export async function downloadFileFromStorage(file: StirlingFileStub): Promise<v
     throw new Error(`File "${file.name}" not found in storage`);
   }
 
-  // StirlingFile is already a File object, just download it
-  downloadBlob(stirlingFile, stirlingFile.name);
+  await downloadFile({
+    data: stirlingFile,
+    filename: stirlingFile.name,
+    localPath: file.localFilePath
+  });
 }
 
 /**
@@ -80,7 +74,7 @@ export async function downloadFilesAsZip(files: StirlingFileStub[], zipFilename?
 
   // Create and download ZIP
   const { zipFile } = await zipFileService.createZipFromFiles(filesToZip, finalZipFilename);
-  downloadBlob(zipFile, finalZipFilename);
+  await downloadFile({ data: zipFile, filename: finalZipFilename });
 }
 
 /**
@@ -120,7 +114,7 @@ export async function downloadFiles(
  * @param filename - Optional custom filename
  */
 export function downloadFileObject(file: File, filename?: string): void {
-  downloadBlob(file, filename || file.name);
+  void downloadFile({ data: file, filename: filename || file.name });
 }
 
 /**
@@ -135,7 +129,7 @@ export function downloadTextAsFile(
   mimeType: string = 'text/plain'
 ): void {
   const blob = new Blob([content], { type: mimeType });
-  downloadBlob(blob, filename);
+  void downloadFile({ data: blob, filename });
 }
 
 /**

frontend/src/core/utils/fileDialogUtils.ts

@@ -0,0 +1,6 @@
+export function getDocumentFileDialogFilter() {
+  return [{
+    name: 'Documents',
+    extensions: ['pdf', 'jpg', 'jpeg', 'png', 'gif', 'tiff', 'bmp', 'html', 'zip']
+  }];
+}