add completed at index

db/migrate/20250615091654_add_submitters_completed_at_index.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class AddSubmittersCompletedAtIndex < ActiveRecord::Migration[8.0]
+  def change
+    add_index :submitters, %i[completed_at account_id]
+  end
+end