Users reported that the API key edit drawer's "Save changes" button
becomes unresponsive after the drawer has been open / idle for a
while: no loading state, no request, no error. Reopening the drawer
restores it because a fresh DOM is created.
The button lived in `SheetFooter` (a portaled Base UI Sheet) and was
linked to the form via the HTML `form='api-key-form'` attribute. Once
the portal/DOM relationship goes stale, the click no longer triggers
the form's submit event, hence the silent failure.
Defensive fix: drop the cross-DOM `form` linkage and call
`form.handleSubmit(onSubmit)` directly via `onClick`. The native
submit path (Enter key, original `<form onSubmit>`) is preserved.
Closes #4858
