Cron jobs

A _cron_jobs record is the whole job: name, a 5-field cron expression, and a raw SQL statement to run on it — editable from the dashboard’s Cron jobs screen or the generic Records API, no match-arm registry and no rebuild for a new job type. Changes are reactive: creating, updating, or deleting a _cron_jobs row takes effect on the live scheduler immediately, no restart. lastRunAt/lastStatus/ lastMessage are written back after every run, including the real driver error on failure, and a job can be run on demand via POST /api/crons/custom:<id>.