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-waybar-nightlight

@@ -0,0 +1,9 @@
+#!/bin/bash
+# ABOUTME: Outputs JSON status for waybar nightlight module.
+# ABOUTME: Shows warm icon when wlsunset is active, cool icon when off.
+
+if pgrep -x wlsunset > /dev/null; then
+    jq -nc '{text: "󰌵", alt: "on", tooltip: "Nightlight: An (5000K)", class: "on"}'
+else
+    jq -nc '{text: "󰌶", alt: "off", tooltip: "Nightlight: Aus", class: "off"}'
+fi