Add backups?

[6r1d]

#13 reminded me it may be better to save the current patches. They appear rarely, but it'll be nicer to have them than not.

I don't know if JSON is optimal here, but that's something: patches_2025-03-24.tar.gz

I think it should be possible to set up a monthly CI job with a script like this (maybe that's a bit complex, but it may be hidden in CI anyway):

audiomasher_backup_script.tar.gz