feat(modules/dgn-console): Add an activation script showing system diffs

modules/dgn-console.nix

@@ -42,6 +42,14 @@ in {
         };
       })
     ];
+
+    system.activationScripts.diff = {
+      supportsDryActivation = true;
+      text = ''
+        ${pkgs.nvd}/bin/nvd --nix-bin-dir=${pkgs.nix}/bin diff /run/current-system "$systemConfig"
+      '';
+    };
+
     programs.bash.promptInit = ''
       FQDN="$(hostname).$(domainname)"
       # Provide a nice prompt if the terminal supports it.
@@ -85,6 +93,5 @@ in {
           --old-bindir $OLDBIN --new-bindir $NEWBIN \
           "$@"
       '');
-
   };
 }