Only the top modal owned the focus trap, but every lower `Modal.Content`
remained an exposed `aria-modal` dialog with reachable controls and a live
iframe — so browse navigation could land in a dialog that is visually covered
and that itself claims the rest of the page is inert.
Non-top contents are now `inert`: out of the accessibility tree and out of
focus order, without unmounting, so each app keeps its bridge and its handshake
and is live the moment it becomes top.
Signed-off-by: cliffhall <cliff@futurescale.com>
beaaad4982