Update NixOS config.

nixosModules/systemd.nix

@@ -0,0 +1,26 @@
+{ config, pkgs, lib, ... }:
+
+{
+
+  systemd.timers."update-flatpak" = {
+  wantedBy = [ "timers.target" ];
+    timerConfig = {
+      OnBootSec = "1m";
+      OnCalendar = "daily";
+      Unit = "update-flatpak.service";
+    };
+  };
+
+  systemd.services."update-flatpak" = {
+    script = ''
+      set -eu
+      ${pkgs.flatpak}/bin/flatpak update --noninteractive --assumeyes
+    '';
+    serviceConfig = {
+      Type = "oneshot";
+      User = "root";
+    };
+    wantedBy = [ "multi-user.target" ]; # Ensure the service starts after rebuild
+  };
+
+}