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>

modules/home/default.nix

@@ -17,6 +17,7 @@
     ./idle.nix      # hyprlock + hypridle, themed from the same JSON
     ./yazi.nix      # flagship TUI file manager, themed + plugins
     ./osd.nix       # swayosd volume/brightness OSD, themed
+    ./nightlight.nix # scheduled blue-light filter (hyprsunset), opt-in
     ./shell.nix     # zsh + starship + bat/eza/zoxide, themed
     ./keys.nix      # gpg-agent (fronts SSH) + pinentry-qt
     ./fastfetch.nix # system info with the themed Nomarchy logo

modules/home/nightlight.nix

@@ -0,0 +1,25 @@
+# Night light — a scheduled blue-light filter via hyprsunset (Hyprland's own
+# gamma/temperature tool). Warm at night, identity (no shift) by day;
+# hyprsunset's time-based `profile` entries handle the schedule and pick the
+# right state on session start. Opt-in via nomarchy.nightlight.enable.
+#
+# The hyprsunset HM service module is provided by home-manager; this only
+# configures it. Override anything with plain services.hyprsunset.* options.
+{ config, lib, ... }:
+
+let
+  cfg = config.nomarchy.nightlight;
+in
+{
+  config = lib.mkIf cfg.enable {
+    services.hyprsunset = {
+      enable = true;
+      settings.profile = [
+        # Daytime: identity = no colour change.
+        { time = cfg.sunrise; identity = true; }
+        # Night: shift to the warm temperature.
+        { time = cfg.sunset; temperature = cfg.temperature; }
+      ];
+    };
+  };
+}

modules/home/options.nix

@@ -157,6 +157,33 @@ in
       '';
     };
 
+    nightlight = {
+      enable = lib.mkEnableOption ''
+        a scheduled blue-light filter (hyprsunset): warm at night, no shift
+        by day. Opt-in; tune the temperature + sunrise/sunset below'';
+
+      temperature = lib.mkOption {
+        type = lib.types.int;
+        default = 4000;
+        example = 3500;
+        description = "Warm colour temperature (K) applied at night — lower is warmer.";
+      };
+
+      sunrise = lib.mkOption {
+        type = lib.types.str;
+        default = "07:00";
+        example = "06:30";
+        description = "Time (HH:MM) the filter turns OFF — daytime, no colour shift.";
+      };
+
+      sunset = lib.mkOption {
+        type = lib.types.str;
+        default = "20:00";
+        example = "21:00";
+        description = "Time (HH:MM) the filter turns ON — warm.";
+      };
+    };
+
     monitors = lib.mkOption {
       type = lib.types.listOf monitorType;
       default = [ ];