Fix 500 callback YouTube: pagina token senza layout admin.

Il layout admin richiedeva admin_logged_in? non disponibile nel callback OAuth.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/controllers/youtube_oauth_callback_controller.rb

@@ -1,7 +1,5 @@
 # Callback OAuth YouTube (HTML). Non usare Api::V1 — ActionController::API non renderizza le view.
 class YoutubeOauthCallbackController < ActionController::Base
-  layout "admin"
-
   def show
     return redirect_to_oauth_error("Codice OAuth mancante") if params[:code].blank?
 
@@ -11,7 +9,7 @@ class YoutubeOauthCallbackController < ActionController::Base
     if ctx[:kind] == :platform
       @refresh_token = tokens[:refresh_token]
       @channel_title = tokens[:channel_title]
-      return render "admin/youtube/platform_token"
+      return render "admin/youtube/platform_token", layout: false
     end
 
     user = User.find(ctx[:user_id])