New page: docs/automation/tasks.md — comprehensive reference for the task
system covering lifecycle, delivery, notifications, audit, CLI commands,
storage, maintenance, and how tasks relate to cron/heartbeat/sessions.
- Add to Mintlify navigation (docs.json) under Automation group
- Clean up engineer's earlier scattered additions in cron-jobs.md,
cron-vs-heartbeat.md, and heartbeat.md to be concise and link to the
new canonical tasks page
- Replace verbose inline explanations with cross-reference links
8a916652e8
