fix: reset host status and failures on requestCrawl
when requestCrawl re-validates an exhausted host via describeServer,
reset its status to 'active' and clear failed_attempts. without this,
exhausted hosts accumulate failures across cronjob cycles and
immediately re-exhaust on a single connection failure.
909 of 3140 tracked hosts were stuck in 'exhausted' state.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>