add preview image url to templates

app/controllers/api/templates_controller.rb

@@ -52,7 +52,7 @@ module Api
     def serialize_params
       {
         include: { author: { only: %i[id email first_name last_name] },
-                   documents: { only: %i[id uuid], methods: %i[url filename] } }
+                   documents: { only: %i[id uuid], methods: %i[url preview_image_url filename] } }
       }
     end
 

config/initializers/active_storage.rb

@@ -4,6 +4,10 @@ ActiveSupport.on_load(:active_storage_attachment) do
   attribute :uuid, :string, default: -> { SecureRandom.uuid }
 
   has_many_attached :preview_images
+
+  def preview_image_url
+    preview_images.joins(:blob).find_by(blob: { filename: '0.jpg' })&.url
+  end
 end
 
 ActiveStorage::LogSubscriber.detach_from(:active_storage) if Rails.env.production?