fix cron scheduling and reminder delivery regressions (#9733)

* fix(cron): prevent timer from allowing process exit (fixes #9694)

The cron timer was using .unref(), which caused the Node.js event
loop to exit or sleep if no other handles were active. This prevented
cron jobs from firing in some environments.

* fix(cron): infer delivery target for isolated jobs (fixes #9683)

When creating isolated agentTurn jobs (e.g. reminders) without explicit
delivery options, the job would default to 'announce' but fail to
resolve the target conversation. Now, we infer the channel and
recipient from the agent's current session key.

* fix(cron): enhance delivery inference for threaded sessions and null inputs (#9733)

Improves the delivery inference logic in the cron tool to correctly handle threaded session keys and cases where delivery is explicitly set to null. This ensures that the appropriate delivery mode and target are inferred based on the agent's session key, enhancing the reliability of job execution.

* fix: preserve telegram topic delivery inference (#9733) (thanks @tyler6204)

* fix: simplify cron delivery merge spread (#9733) (thanks @tyler6204)

CHANGELOG.md

@@ -50,6 +50,7 @@ Docs: https://docs.openclaw.ai
 - Cron: accept epoch timestamps and 0ms durations in CLI `--at` parsing.
 - Cron: reload store data when the store file is recreated or mtime changes.
 - Cron: deliver announce runs directly, honor delivery mode, and respect wakeMode for summaries. (#8540) Thanks @tyler6204.
+- Cron: correct announce delivery inference for thread session keys and null delivery inputs. (#9733) Thanks @tyler6204.
 - Telegram: include forward_from_chat metadata in forwarded messages and harden cron delivery target checks. (#8392) Thanks @Glucksberg.
 - Telegram: preserve DM topic threadId in deliveryContext. (#9039) Thanks @lailoo.
 - macOS: fix cron payload summary rendering and ISO 8601 formatter concurrency safety.