Add Zsh shell to Darwin services and setup Harald's dev environment

Add Zsh to the list of available shells in the Darwin services module.
Introduce new Nix configurations for aarch64-darwin, including system packages and font settings.
Set up user-specific environment for Harald on aarch64-darwin system.

modules/darwin/services/base/default.nix

@@ -41,6 +41,7 @@ in
       shells = [
         pkgs.fish
         pkgs.bash
+        pkgs.zsh
       ];
     };