* fix(cron): comprehensive cron scheduling and delivery fixes
- Fix delivery target resolution for isolated agent cron jobs
- Improve schedule parsing and validation
- Add job retry logic and error handling
- Enhance cron ops with better state management
- Add timer improvements for more reliable cron execution
- Add cron event type to protocol schema
- Support cron events in heartbeat runner (skip empty-heartbeat check,
use dedicated CRON_EVENT_PROMPT for relay)
* fix: remove cron debug test and add changelog/docs notes (#11641) (thanks @tyler6204)