User-provided ISO timestamps like '2026-02-03T14:00' (no timezone)
were stored naive. The _ensure_aware() helper at check time interprets
naive datetimes using the current system timezone, but if the system
timezone changes between job creation and checking, the job fires at
the wrong time.
Fix: call dt.astimezone() at parse time to immediately stamp the
datetime with the local timezone. The stored value is now always
timezone-aware, so it's stable regardless of later timezone changes.
5301c01776