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/bin/moonarch-nightlight

@@ -0,0 +1,12 @@
+#!/bin/bash
+# ABOUTME: Toggles wlsunset night light on/off.
+# ABOUTME: Kills or restarts wlsunset process, signals waybar for refresh.
+
+if pgrep -x wlsunset > /dev/null; then
+    pkill -x wlsunset
+else
+    wlsunset -T 6500 -t 5000 -S 00:00 -s 00:01 &
+    disown
+fi
+
+pkill -RTMIN+11 waybar