feat(darwin): auto upgrade homebrew

modules/darwin/apps.nix

@@ -90,7 +90,8 @@ in {
     enable = true; # disable homebrew for fast deploy
 
     onActivation = {
-      autoUpdate = true;
+      autoUpdate = true; # Fetch the newest stable branch of Homebrew's git repo
+      upgrade = true; # Upgrade outdated casks, formulae, and App Store apps
       # 'zap': uninstalls all formulae(and related files) not listed in the generated Brewfile
       cleanup = "zap";
     };