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.

ui/src/ui/app-defaults.ts

@@ -21,9 +21,9 @@ export const DEFAULT_CRON_FORM: CronFormState = {
   everyUnit: "minutes",
   cronExpr: "0 7 * * *",
   cronTz: "",
-  sessionTarget: "main",
+  sessionTarget: "isolated",
   wakeMode: "next-heartbeat",
-  payloadKind: "systemEvent",
+  payloadKind: "agentTurn",
   payloadText: "",
   deliveryMode: "announce",
   deliveryChannel: "last",