fix(home-manager): use correct theme name

[eljamm]

Summary

The theme name does not correctly match the one from catppuccin-gtk which should be catppuccin-${FLAVOR}-${ACCENT}-${SIZE}+${TWEAKS} as the Usage docs specify.

Changes

• Name is all lower case now
• Order changed from flavor-size-accent-gtkTheme to flavor-accent-size+tweaks

[eljamm]

If I didn't mess up, [ "normal" "black" "rimless" ] should become "default+black+rimless" with this change.

[eljamm]

Well, turns out I did mess up, but it should work now.

[eljamm]

So apparently it's just enough to append the tweaks at the end. In the derivation result, the names were being seperated by , and not + so I changed that as well.

I tested this on my machine and everything works great.