rEFind: add target

[gaelj]

Description

The release notes of NixOS 25.11 mention that rEFind can now be used as boot manager, so I activated it in place of systemd-boot, hoping to get a beautiful graphical boot menu. Unfortunately with the default settings it's still a simple text menu.

It would be nice if Stylix could apply its theming to the rEFind boot menu. Even better, would be to have a graphical menu. More info at https://www.rodsbooks.com/refind/themes.html

Submission Checklist

• I assert that this issue is relevant to Stylix
• I assert that this is not a duplicate of an existing issue