`start()` asked "Install it now so the gateway starts on login?" with default Yes, then called
`install()` which asked two more default-Yes questions; on a redirected stdin (`< /dev/null`,
scripts, agent tool calls) all three answered themselves and a bare `start` wrote a Startup-folder
login item, spawned the gateway, and start() spawned it a second time (#113977).
- The persistence question is answered only explicitly: `HERMES_GATEWAY_INSTALL_START_ON_LOGIN`
(which start() never consulted before) or a prompt on a real TTY. Without a TTY, or under
`HERMES_NONINTERACTIVE=1`, the answer is No: the gateway starts, nothing persistent is written,
and the explicit `hermes gateway install` command is printed.
- Declining on a TTY also starts the gateway — the command is `start`; only persistence was declined.
- A Yes hands `start_now=True, start_on_login=True` to install(), which spawns and reports (including
the UAC hand-off), so start() no longer double-spawns and no longer prints the false
"Gateway install did not complete in this process" after an install that was skipped by intent.
- `install --no-start-on-login` without `--start-now` now hints `hermes gateway run` instead of the
`hermes gateway start` that used to offer the very auto-start just declined.
Supersedes #113981 (@KoNit-K), which flipped the first prompt's non-TTY default but left the
env override, the hint text and the false warning in place.
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