feat: add wlsunset nightlight toggle with Waybar module

Add blue light filter support via wlsunset, toggleable through a Waybar
module in the brightness group. Nightlight icon is the primary element,
backlight slider expands on click.

- Add wlsunset package to official.txt
- Add moonarch-nightlight toggle script (kill/restart wlsunset)
- Add moonarch-waybar-nightlight status script (JSON output)
- Add custom/nightlight module to group/brightness in Waybar config
- Add Catppuccin Yellow highlight for active nightlight state
- Add wlsunset autostart in Niri config (5000K night temperature)

defaults/xdg/waybar/style.css

@@ -257,6 +257,10 @@ widget widget>* {
     color: alpha(@theme_selected_bg_color, 0.9);
 }
 
+#custom-nightlight.on {
+    color: #f9e2af;
+}
+
 menu {
     border-radius: 4px;
 }