Reap agent cloud instances abandoned in a non-terminal status

Cron endpoint that finalizes agent cloud instances left in a non-terminal status (queued or running) past their deadline by a pod that crashed or was lost without writing a terminal status. Terminates never-started (queued) instances, fails abandoned (running) instances, and releases the rate-limit quota slot each held. Authorization handled by CloudSchedulerAuthorizationFilter in web.xml.