Turbo Frames - Form Submission Loading States

Premise In the Loading Spinner challenge, we added busy indicators for Turbo Frame navigations — links that swap frame content asynchronously. But what about forms? When a user submits a form inside a Turbo Frame, Turbo handles the request and swaps the response, but gives zero visual feedback while it’s in flight. The button stays clickable, nothing changes on screen, and the user is left…