hermes update hangs on input() when run from cron, scripts, or piped
contexts. Check both stdin and stdout isatty(), catch EOFError as a
fallback, and print guidance to run 'hermes config migrate' later.
Co-authored-by: phippsbot-byte <phippsbot-byte@users.noreply.github.com>
`hermes update` crashed with CalledProcessError when run on a local-only
branch (e.g. fix/stoicneko) because `git rev-list HEAD..origin/{branch}`
fails when origin/{branch} doesn't exist. Now verifies the remote branch
exists first and falls back to origin/main.