feat(cron): add script_only mode to bypass LLM entirely

[Znarkus]

Summary

When a cron job has script_only=true and a script configured, the script stdout is delivered directly as the final message — no LLM is invoked at all.

This saves tokens and ensures 100% consistent formatting for jobs where the script already produces the final user-facing output. The [SILENT] marker still works to suppress delivery.

Changes

• cron/scheduler.py — Early return in run_job() for script_only jobs: runs the script via _run_job_script() and returns output directly
• cron/jobs.py — script_only: bool parameter in create_job(), persisted in the job dict
• tools/cronjob_tools.py — Schema property, handler wiring, create/update support, formatted output

Usage

# Create a script-only cron job (no LLM, no tokens)
cronjob(action='create', script='my_check.py', script_only=True, schedule='0 * * * *', name='Hourly check')

# Update existing job to script-only
cronjob(action='update', job_id='abc123', script_only=True)

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