Multiple Hermes installations on the same machine now get unique
systemd service names:
- Default ~/.hermes → hermes-gateway (backward compatible)
- Custom HERMES_HOME → hermes-gateway-<8-char-hash>
Changes:
- Add get_service_name() in hermes_cli/gateway.py that derives a
deterministic service name from HERMES_HOME via SHA256
- Replace all hardcoded 'hermes-gateway' systemd references with
get_service_name() across gateway.py, main.py, status.py, uninstall.py
- Add HERMES_HOME env var to both user and system systemd unit templates
so the gateway process uses the correct installation
- Update tests to use get_service_name() in assertions