fix(macos): install disk-inventory-x via Homebrew cask

Use the Homebrew cask on Apple Silicon because the nixpkgs package is x86_64-darwin only, and document the reason inline to prevent future regressions.

Made-with: Cursor

nixos/hosts/daniel-macbook-air.nix

@@ -38,6 +38,7 @@ in {
     enable = true;
     casks = [
       "google-chrome"
+      "disk-inventory-x" # Apple Silicon uses Homebrew; nixpkgs package is x86_64-darwin only.
     ];
     onActivation.cleanup = "zap";
   };