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.

systems/aarch64-darwin/m4/default.nix

@@ -0,0 +1,23 @@
+{ lib, pkgs, ... }:
+
+with lib.metacfg;
+{
+  metacfg = {
+    suites = {
+      common = enabled;
+    };
+  };
+
+  environment.systemPackages = with pkgs; [
+    # azure-cli
+    kubectl
+    kubectx
+    k9s
+    attic-client
+    ollama
+  ];
+
+  users.users.harald.shell = pkgs.fish;
+
+  system.stateVersion = 4;
+}