Adds WebUI controls to manage the messaging gateway lifecycle without a
terminal. _handle_gateway_lifecycle routes start/stop/restart to the
existing platform-aware `hermes gateway {action}` CLI via a list-argv
subprocess (no shell), scoped to the active profile, with bounded
timeout/error handling and a status-card refresh. Auth + CSRF gated;
profile name charset-validated; stdout/stderr never leaked to the client.
Maintainer hardening (warm-up SHOULD-FIX): added _GATEWAY_ACTION_LOCK, a
server-side single-flight guard. The client disables its button in-flight,
but a scripted authed client could otherwise fire overlapping
start/stop/restart calls and spawn concurrent gateway subprocesses. A
non-blocking acquire now returns 409 on contention (mirrors the self-update
_apply_lock pattern), released in finally. Added a regression test
(toothless-checked: without the lock the 2nd action spawns a subprocess +
returns 200).
Cross-platform: delegates to the mature hermes_cli gateway subcommand
(systemctl/launchctl), pathlib paths, PYTHONUTF8=1 + BROWSER=echo in env.
Co-authored-by: Rod Boev <rod.boev@gmail.com>
a41a1bf393