move options back out to their config files, improve documentation

modules/features/nixos/stylix.nix

@@ -1,4 +1,8 @@
 { inputs, self, ... }: {
+  imports = [ (inputs.helpers.mkMirroredModulesFlakeModule "graphicsOptions" ({ lib, ... }: {
+    options.features.nixos.stylix.enable = lib.mkEnableOption "Stylix";
+  })) ];
+
   flake.nixosModules.graphics = { pkgs, lib, config, ... }: {
     imports = [
       inputs.stylix.nixosModules.stylix