Rearrange the config structure

system/darwin/defaults.nix

@@ -0,0 +1,30 @@
+{ config, pkgs, ... }:
+
+{
+  imports = [
+    ../../modules/homebrew.nix
+  ];
+
+  # Set primary user for system preferences
+  system.primaryUser = "yanlin";
+  
+  # Menu bar spacing configuration using activation scripts
+  # Uses sudo to run as user since activation now runs as root
+  # NSStatusItemSpacing controls horizontal spacing between menu bar items
+  # NSStatusItemSelectionPadding controls padding inside selection overlay
+  system.activationScripts.extraActivation.text = ''
+    echo "Setting menu bar spacing preferences..."
+    sudo -u yanlin defaults -currentHost write -globalDomain NSStatusItemSpacing -int 10
+    sudo -u yanlin defaults -currentHost write -globalDomain NSStatusItemSelectionPadding -int 5
+    
+    echo "Disabling Spotlight indexing..."
+    # Disable Spotlight indexing for all volumes
+    # WARNING: This will break Mail.app search, Time Machine, and other features
+    # To re-enable: sudo mdutil -a -i on
+    sudo mdutil -a -i off
+    
+    # Erase existing Spotlight index to free up disk space
+    echo "Erasing existing Spotlight index..."
+    sudo mdutil -E /
+  '';
+}