feat(cron): enhance one-shot job behavior and CLI options

- Default one-shot jobs to delete after success, improving job management.
- Introduced `--keep-after-run` CLI option to allow users to retain one-shot jobs post-execution.
- Updated documentation to clarify default behaviors and new options for one-shot jobs.
- Adjusted cron job creation logic to ensure consistent handling of delete options.
- Enhanced tests to validate new behaviors and ensure reliability.

This update streamlines the handling of one-shot jobs, providing users with more control over job persistence and execution outcomes.

src/agents/tools/cron-tool.ts

@@ -206,6 +206,7 @@ LEGACY DELIVERY (payload, only when delivery is omitted):
 CRITICAL CONSTRAINTS:
 - sessionTarget="main" REQUIRES payload.kind="systemEvent"
 - sessionTarget="isolated" REQUIRES payload.kind="agentTurn"
+Default: prefer isolated agentTurn jobs unless the user explicitly wants a main-session system event.
 
 WAKE MODES (for wake action):
 - "next-heartbeat" (default): Wake on next heartbeat