fix(gateway): restart via service in containers

[he-yufeng]

Summary

Closes #25217.

/restart currently uses a detached helper whenever the gateway is not running under systemd. That works for a normal shell process, but not for Docker/Podman: once the gateway exits as PID 1, the container stops and the detached helper goes with it.

This routes container restarts through the existing service-restart path instead:

• systemd: unchanged, detached=False, via_service=True
• Docker/Podman: now also detached=False, via_service=True
• plain non-container process: still uses the detached helper

The service path exits with the existing restart code, so a Docker/Podman restart policy such as unless-stopped or on-failure can bring the container back.

Tests

python -m py_compile gateway\run.py tests\gateway\test_restart_notification.py tests\gateway\test_restart_drain.py
python -m ruff check gateway\run.py tests\gateway\test_restart_notification.py tests\gateway\test_restart_drain.py
python -m pytest -o addopts='' tests\gateway\test_restart_notification.py tests\gateway\test_restart_drain.py::test_restart_command_while_busy_requests_drain_without_interrupt -q --basetemp .tmp\pytest -p no:cacheprovider

Result: 27 passed.

Note: the full tests\gateway\test_restart_drain.py file has an existing Windows-only failure in test_launch_detached_restart_command_uses_setsid: this Windows run enters the sys.executable -c detached watcher branch, while that test expects the POSIX setsid bash path.

[alt-glitch]

Duplicate of #25219 — same fix (Docker/Podman container detection for /restart service path) targeting the same issue #25217. Also competes with #25264. This PR uses is_container() from hermes_constants and includes test updates.

[liuhao1024]

Heads up: duplicate of #25264

PR #25264 solves the same issue (#25217) but takes a cleaner approach — it imports the existing is_container() utility from hermes_constants instead of inlining the Docker/Podman file checks. The shared helper is more maintainable if additional container runtimes need detection in the future.

Both PRs have test coverage. Worth consolidating into one.

[he-yufeng]

Thanks for the heads-up. Agreed this overlaps with #25219 / #25264 and targets the same restart path issue. Closing this one to avoid another competing duplicate.