refactor: use preview image for featured arts

- Use `preview_image(:large).processed` instead of `image`
  for displaying featured arts.

This change improves the performance of the homepage by
displaying a processed preview image instead of the original,
potentially large, image. This reduces the initial load time
and improves user experience.

app/views/home/index.html.erb

@@ -3,7 +3,7 @@
   <section class="h-screen-90 relative overflow-hidden">
     <% if @featured_arts.first&.image&.attached? %>
       <div class="absolute inset-0">
-        <%= image_tag @featured_arts.first.image, class: "w-full h-full object-cover" %>
+        <%= image_tag @featured_arts.first.preview_image(:large).processed, class: "w-full h-full object-cover" %>
         <div class="absolute inset-0 bg-gradient-to-r from-base-100/90 to-base-100/50"></div>
       </div>
     <% end %>