v3.0.2: fix(ConfirmDeleteDialog): Display thumbnails correctly

The thumbnail display logic was broken.

- Modified `app_frontend/src/ConfirmDeleteDialog.tsx` to fetch and display thumbnails correctly.
- Added `thumbnailUrl` variable to map the thumbnail data to its corresponding file.
- Updated the `img` tag `src` attribute to use the correct thumbnail url from `thumbnailMap`.
- The thumbnail queries are cached, and the file data is used as the key.