add nix settings and dir colors for MacOS

system/macos/nix.nix

@@ -0,0 +1,12 @@
+{ config, lib, ... }:
+{
+  # Enable the Nix package manager
+  nix = {
+    enable = true;
+
+    settings = {
+      # Configure trusted users who can perform privileged Nix operations
+      trusted-users = lib.mkForce [ "@admin" "${config.system.primaryUser}" ];
+    };
+  };
+}