The uninstaller's gateway cleanup was incomplete:
- Linux only (ignored macOS launchd)
- Only checked user systemd scope (missed system services)
- Didn't kill standalone gateway processes (hermes gateway run)
- Missing DBUS env setup for headless servers
Now delegates to gateway.py's existing machinery:
1. Kill any standalone gateway processes (all platforms)
2. Linux: stop + disable + remove both user AND system systemd services
3. macOS: unload + remove launchd plist
4. Warns (instead of silently failing) when system service needs sudo