Move Night Light onto a first-party nightlight service

Same treatment as Stay Awake: the indicator polled the toggle CLI over
a Process with a timer to paper over the race after clicking, and the
CLI ended by asking the shell to refresh every indicator over IPC. A new
omarchy.nightlight service owns hyprsunset instead - it probes the
temperature on startup, applies changes itself for in-shell toggles, and
answers on the nightlight IPC target. The indicator becomes a plain
binding. The CLI still drives hyprctl directly so keybindings, the menu,
and ssh work without the shell, but now just nudges the service to
re-probe since hyprsunset has no state file to watch.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

bin/omarchy-toggle-nightlight

@@ -49,4 +49,4 @@ else
   hyprctl hyprsunset temperature $OFF_TEMP
 fi
 
-omarchy-shell -q omarchy.indicators refresh
+omarchy-shell -q nightlight refresh