Banner file type is forced to png

This is more of a combined issue between the website and possibly the server and the onboard, but while it hasn't become an issue yet, all banners uploaded are automatically given the .png file type. This became obvious when loading the banner for Dev-Maze into Godot as it just won't do it, but changing the file type to a .jpg fixes it.
currently, MonoGame does not seem to care and will load it correctly anyway, but it would be better if the downloaded banners had the right file extension.
Also, more of a website issue, but there is no specification that the uploaded image has to be a .png

Trace banner upload and download handling across the website, server, and onboard components; the issue names no files or entry points. Reproduce the extension problem with a JPG banner in Godot, then verify that downloaded banners preserve their actual type and that the upload requirement is specified.

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