Move Nix files back to the root of the project

hosts/t490/services/redshift.nix

@@ -0,0 +1,31 @@
+{ config, lib, ... }:
+
+with lib;
+
+let
+  cfg = config.nixosModules.redshift;
+in
+{
+  options.nixosModules.redshift.enable = mkEnableOption "Enable redshift";
+
+  config = mkIf cfg.enable {
+    location = {
+      latitude = 51.48;
+      longitude = -3.17;
+    };
+
+    services.redshift = {
+      enable = true;
+
+      brightness = {
+        day = "1";
+        night = "1";
+      };
+
+      temperature = {
+        day = 5500;
+        night = 3700;
+      };
+    };
+  };
+}