Revalidate DOI Suffix on Publishment for Articles
Upon publishing an article that uses a custom DOI, it's possible that the DOI suffix was valid (no other DOI had the same prefix + suffix) when it was input, but it was registered afterwards before publishing occurs. So, before attempting to register the DOI in the publishment phase, check to make sure the DOI doesn't exist.
If it does, fail the publishment and show a toast on the frontend with the text "The custom DOI suffix is already used by an existing DOI."