The work would be only in ish_manager repository. When uploading photos to a gallery, ajax returns just the thumbnail. It needs to return a more detailed partial, with links to “large”, “original” uploaded file.
On the same page you can already see such a partial, with red border. You can reuse that.
Bonus: when uploading, say, 20 images, the ajax-returned thumbs are all in one line. They should wrap to multi-line (probably best to do it with flexbox, flex-wrap).
Bonus: display the count of uploaded images somewhere.
Bonus: if a file fails to upload, show the filename or the failed file, and an error. You can fail the upload if the file is too large, the failure is usually the timeout.