feat(nixos): migrate system configuration

configs/nixos/modules/desktop/session/login.nix

@@ -0,0 +1,23 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+# Text login: greetd running the tuigreet greeter, which starts the session
+# through the universal Wayland session manager.
+let
+  cfg = config.modules.desktop.session.login;
+in
+{
+  options.modules.desktop.session.login.enable = lib.mkEnableOption "greetd with the tuigreet text greeter";
+
+  config = lib.mkIf cfg.enable {
+    services.greetd = {
+      enable = true;
+      settings.default_session.command =
+        "${lib.getExe pkgs.tuigreet} --time --remember "
+        + "--cmd 'uwsm start -e -D Hyprland hyprland.desktop'";
+    };
+  };
+}