create shared niri config, refactor generic feature modules

modules/features/applications/gui/floorp.nix

@@ -14,7 +14,7 @@
   flake.homeModules.graphics = { pkgs, lib, config, ... }: {
     config = lib.mkIf (config.features.applications.gui.floorp.enable) (
     let
-      firefox-addons = with pkgs; inputs.firefox-addons.packages.${pkgs.stdenv.hostPlatform.system};
+      firefox-addons = inputs.firefox-addons.packages.${pkgs.stdenv.hostPlatform.system};
     in {
       programs.floorp = {
         enable = true;