* 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.