#1 Fix execution duration calculation - started_at overwritten on wake-up

Bug: In orchestrator.py line 331, whenever a workflow wakes from sleep and transitions to running state, it unconditionally updates started_at = datetime.now(). This overwrites the original start time, causing duration_ms to only reflect the time of the final wake-up cycle, not the total workflow duration. Fix: Only set started_at if it hasnt been set before.