chore: add comment for response format

app/controllers/facebook/delete_controller.rb

@@ -10,6 +10,10 @@ class Facebook::DeleteController < ApplicationController
     Webhooks::FacebookDeleteJob.perform_later(id_to_process)
     status_url = "#{app_url_base}/facebook/confirm/#{id_to_process}"
 
+    # IMPORTANT: Do not change the response format below.
+    # Facebook's Data Deletion Request system specifically expects responses in this format
+    # with a 'url' for status confirmation and a 'confirmation_code' field.
+    # See: https://developers.facebook.com/docs/development/create-an-app/app-dashboard/data-deletion-callback/#implementing
     render json: { url: status_url, confirmation_code: id_to_process }, status: :ok
   rescue InvalidDigestError
     render json: { error: 'Invalid signature' }, status: :unprocessable_entity