fix(cron): share isolated announce flow + harden cron scheduling/delivery (#11641)

* 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)

src/gateway/protocol/schema/cron.ts

@@ -107,6 +107,7 @@ export const CronJobStateSchema = Type.Object(
     ),
     lastError: Type.Optional(Type.String()),
     lastDurationMs: Type.Optional(Type.Integer({ minimum: 0 })),
+    consecutiveErrors: Type.Optional(Type.Integer({ minimum: 0 })),
   },
   { additionalProperties: false },
 );