Update custom trigger schedule

patch

https://example.com/config-triggers/v1/trigger-schedules/{scheduleId}

Merge-patch semantics: only the fields present in the request body are changed. weekDays, when present, replaces the whole week (days not listed become unscheduled). Sending no effective change returns 200 with the current schedule and writes nothing. Built-in schedules cannot be modified. Concurrent updates are last-writer-wins.