[Mutual Games] Add horizontal scroll bar to grouped friend list

[Jeshibu]

Discussed in #76

^{Originally posted by Mr-Crotchrot May 29, 2025}
I done goofed and accidentally added one friend under another friend's listing. I've added the second friend to their own category, but there's no tag for their name.

I can't figure out for the life of me how to remove someone from the right window after dragging them from the left window.