feat: add wlsunset home-manager module for Wayland night light

Replace the manual wlsunset package + commented exec-once with a proper
home-manager services.wlsunset module tied to hyprland-session.target.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

nixos/wlsunset.nix

@@ -0,0 +1,17 @@
+{ config, pkgs, lib, makeEnable, ... }:
+makeEnable config "myModules.wlsunset" true {
+  home-manager.sharedModules = [
+    {
+      services.wlsunset = {
+        enable = true;
+        latitude = 37.7;
+        longitude = -122.4;
+        temperature = {
+          day = 6500;
+          night = 4000;
+        };
+        systemdTarget = "hyprland-session.target";
+      };
+    }
+  ];
+}