Add back link to cards form

As we normally do in other places.

app/controllers/admin/site_customization/cards_controller.rb

@@ -2,6 +2,7 @@ class Admin::SiteCustomization::CardsController < Admin::SiteCustomization::Base
   include Admin::Widget::CardsActions
   load_and_authorize_resource :page, class: "::SiteCustomization::Page"
   load_and_authorize_resource :card, through: :page, class: "Widget::Card"
+  helper_method :index_path
 
   def index
   end