* fix: purge expired thread_wakeup crons
One-shot wakeup crons set an end_time that stops re-firing but the cron
row is never deleted, so dead rows accumulate (86 in prod). Add a purge
that deletes thread_wakeup crons past their end_time, called
opportunistically before scheduling a new wakeup, plus a one-time
backfill script. Conservative: matches only kind=thread_wakeup with a
past end_time.
* chore: retrigger Open SWE review
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Co-authored-by: open-swe[bot] <open-swe@users.noreply.github.com>
(cherry picked from commit 9e5a1924ef306269322c31342a1831e57831cfee)
