emacs: Install modus-themes via Nix

For some weird reason the theme broke. I suspect it is the latest cl-lib
removal, and Nixpkgs is probably not updated with it just yet. So, at
least it is working via Nix for now. Welcome to Emacs, cheers.

modules/emacs/doom/config.org

@@ -137,7 +137,7 @@ Tangle ~packages.el~ from within org-mode.
 
 (package! org-wild-notifier)
 
-(package! modus-themes)
+(package! modus-themes :type 'built-in :built-in 'prefer)
 
 (package! eglot :type 'built-in :built-in 'prefer)
 

modules/emacs/emacs.nix

@@ -49,6 +49,7 @@ in
         vterm
         all-the-icons
         treesit-grammars.with-all-grammars
+        modus-themes
       ];
     };
   };