fix: Switch macOS to Universal theme

[MikeRatcliffe]

Fixes #23

[victorwads]

@MikeRatcliffe i reviwed the PR, its ok.
I will just ask you to add de Version Info on PR, version on Version files and ChangeLog to Version 0.4.0.
(adds a new feature, so incrise middle version)

The Version files are:

• CMakeList.txt
• flake.nix
• macOs/Info.Plist

And Changelog on XML File:

• io.github.glaumar.QRookie.metainfo.xml

Then i could just Accept your MR and Generate Signed MacOs Versions.

Note: nix build stoped working, but a thing that there is nothing to do with your PR.