There should be a way for a volunteer admin to extract the IFComp big zip

[dfabulich]

As I understand it, we currently have no way for a volunteer admin to extract "big zip" files, like the kind we get from IFComp. (Other comps give us big zips, too.)

In 2024, @jtn20 worked around this by downloading the IFComp2024 zip, extracting it, and manually uploading the individual subzips, then putting each subzip through the normal volunteer process. That worked, but that's… very painful.

I believe in other years @DavidKinder has logged into the machine directly to extract the zip. That works, but it depends on David (and/or @erkyrath?) to be available to do it.

I think we'd want the admin tool to extract big zips into incoming or unprocessed or something, and then we can use the admin tool the rest of the way from there.