dialoguer::Confirm::interact() puts the terminal into raw mode, which
causes the prompt to return immediately without waiting for user input
in some terminal environments. Replace with std::io::stdin().read_line()
which blocks reliably on a full line of input.
Also fix the interactive detection to check both stdin and stderr are
TTYs (matching the pattern used in gateway_select), and restore the
'volume only' status label and image info in the prompt.
* feat(sandbox): add gpu sandbox scheduling support
Allow sandbox creation to request GPU resources explicitly or infer them from GPU image names. This wires GPU intent through bootstrap, validates gateway support, and adds dedicated GPU E2E coverage for follow-up cluster testing.
Drew Newberry