Address Greptile review: add test coverage for runServiceStart path.
The error message copy-paste issue was already fixed in the DRY refactor
(uses params.serviceNoun instead of hardcoded 'restart').
When 'openclaw gateway restart' is run with an invalid config, the new
process crashes on startup due to config validation failure. On macOS,
this causes Full Disk Access (TCC) permissions to be lost because the
respawned process has a different PID.
Add getConfigValidationError() helper and pre-flight config validation
in both runServiceRestart() and runServiceStart(). If config is invalid,
abort with a clear error message instead of crashing.
The config watcher's hot-reload path already had this guard
(handleInvalidSnapshot), but the CLI restart/start commands did not.
AI-assisted (OpenClaw agent, fully tested)
