fix(pi-sentinel): resume PR polling after busy-skip stall

A PR sentinel whose poll timer fired mid-turn was silently dead:
pollEntry returns early when the agent is busy, consuming the timer
without rescheduling, and the setIdle catch-up only revived watches
(waiting/failing) and never-polled PRs. A healthy attached PR (passing,
or actionable failing) matched none of those conditions and never
polled again. Turns routinely exceed the 60s default interval, so this
killed most PR sentinels in real use.

The catch-up now also revives any PR entry whose timer was consumed
(missed poll), while entries with a pending timer keep their schedule.