fix: use autoupgrade only on AC

utils/modules/autoupgrade.nix

@@ -1,6 +1,13 @@
-{ config, ... }:
+{ config, lib, pkgs, ... }:
 
 {
   system.autoUpgrade.enable = true;
   system.autoUpgrade.allowReboot = false;
+
+  # Skip auto-upgrade when on battery to save power
+  systemd.services.nixos-upgrade = {
+    unitConfig = {
+      ConditionACPower = true;
+    };
+  };
 }