Pause or resume the scheduler

Pauses or resumes scheduler-driven run creation for every DAG at once. Admin only.

Pausing has the same effect as suspending every DAG by hand. Manual, webhook, and sub-DAG runs keep working. Queued scheduler-managed runs are aborted and dequeued, catch-up windows are discarded rather than deferred, and nothing replays on resume. One-off schedules stay pending and fire late once the scheduler resumes.