feat(nightlight): scheduled blue-light filter via hyprsunset

Add nomarchy.nightlight (opt-in): a scheduled colour-temperature shift via
the HM services.hyprsunset module -- warm (.temperature, default 4000K) at
night, identity (no shift) by day, switching at .sunset / .sunrise. Two
time-based hyprsunset profiles, so hyprsunset handles the schedule and the
on-login state. New modules/home/nightlight.nix, imported in the home module.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/ROADMAP.md

@@ -289,9 +289,15 @@ how to override it. Items marked ✓ are shipped.
   switching** of the *same* outputs (Hyprland's per-output rules cover the
   common "external connects → arrange" case, not multi-layout toggles), and
   optionally workspace-to-monitor binding.
-- **Night light / blue-light filter:** schedulable colour-temperature shift
-  via `hyprsunset` (Hyprland-native; wlsunset/gammastep are alternatives) —
-  sunset/sunrise or a fixed schedule, with a menu + Waybar toggle.
+- ✓ **Night light / blue-light filter:** `nomarchy.nightlight` (opt-in) —
+  a scheduled colour-temperature shift via `hyprsunset` (Hyprland-native),
+  warm at night, identity (no shift) by day. `modules/home/nightlight.nix`
+  drives the HM `services.hyprsunset` with two time-based profiles
+  (`sunrise` → identity, `sunset` → `temperature`), so hyprsunset handles the
+  schedule and the on-login state. Needs an on-hardware check that hyprsunset
+  applies the active profile at session start. Remaining (optional): a menu +
+  Waybar toggle to force it on/off, and geo (lat/long) auto sunset/sunrise
+  (would mean wlsunset, which schedules by location).
 - **Keyboard layouts (per-device + switching):**
   - ✓ **Per-device declarative layout:** `nomarchy.keyboard.devices`
     (`{ "<hyprctl-device-name>" = { layout; variant; }; }`) generates Hyprland