feat: Use GNOME instead of KDE/Plasma
Plasma 6 has several issues:
- Exposes an HDR flag which doesn't work.
- Windows sometimes don't fill the screen when full-screened.
- KDE apps hijack XDG MIME associations.
Issues which could be fixed by configuration alone:
- Unfamiliar keyboard shortcuts for things like window management.
This reverts commit 29f94b7f.