kickCheckInterval not cleared in shutdown()

Found incidentally while writing MSG-336 (blackboard timeout watchdog): kickCheckInterval is created at hub.mjs:10027 but is never cleared in shutdown() alongside the other five watchdog intervals (pmQueueAll, silenceInterval, bsStuckInterval, busyNudgeInterval, contactEscalateInterval all have a matching clearInterval; kickCheckInterval does not). Leaked timer on SIGTERM only - does nothing visible in normal operation, but is inconsistent with every sibling interval's cleanup. One-line fix: add 'if (kickCheckInterval) clearInterval(kickCheckInterval);' beside the other clearInterval calls in shutdown().