Add niri module

- An overridden `niri.service` is provided, so that systemd does not take
over autostart and try to start things *before* we have an XWayland server running.
- Somehow `wlsunset` is still not working, might need some investigation into why.

home/modules/programs/my-kitty/default.nix

@@ -74,7 +74,7 @@ with lib;
         # Background color and transparency
         background =
           if isNull cfg.background then {
-            background_opacity = "0.85";
+            background_opacity = "0.93";
             dynamic_background_opacity = true;
           } else {
             background_image = "${cfg.background}";