The delete button used type=button + requestSubmit() to trigger the form,
which did not reliably fire SvelteKit's enhance submit listener. Replaced
with a type=submit button and an async enhance callback that guards with
the confirm dialog and calls cancel() on rejection.
Also clears the unsaved-changes dirty flag before the redirect so
beforeNavigate doesn't silently block the post-delete navigation.
Closes#277
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
