- Add execute_scheduled_task helper that fetches task info and dispatches
by target_type (agent/hand/workflow)
- Replace STUB warn+simple-UPDATE with full execution flow: dispatch task,
then update state with interval-aware next_run_at calculation
- Update next_run_at using interval_seconds for recurring tasks instead
of setting NULL
- Fix pre-existing cache.rs borrow-after-move bug (id.clone() in insert)
4e3265a853