Fixes#1005
Without linger, user-level systemd services stop when the SSH session
ends — even though systemctl --user status shows active (running).
Changes to systemd_install():
- Try loginctl enable-linger automatically (succeeds when the process
has the required privileges)
- If loginctl fails (no privileges), print a clear, copy-pasteable
warning with the exact command the user must run
New helper: _ensure_linger_enabled()
- Fast path: checks /var/lib/systemd/linger/<user> (no subprocess)
- Auto-enable: loginctl enable-linger <user>
- Fallback: actionable warning with sudo command + restart instructions
Tests: 4 new tests in TestEnsureLingerEnabled, 205 passed total
* fix(gateway): surface missing linger in status and doctor
Warn when a systemd user gateway service has linger disabled so users can
spot the common 'gateway sleeps after logout' deployment issue from both
hermes doctor and hermes gateway status.
* fix(gateway): check linger status after install
After installing the systemd user service, report whether linger is
already enabled instead of always printing the generic hint. This makes
post-install guidance match the user's actual deployment state.
