Async Action Demo

Clicking the button below calls core/demo_async.php, which runs xcrud_demo_generate_report() (see functions.php) - a deliberately slow (10 second sleep()) stand-in for something like a real report export, a batch update, or an external API call. The button shows the same spinner every Save/Delete button already uses for the whole 10 seconds, stays disabled so it can't be clicked twice, then shows a toast once the request resolves.