Manage queue operations

Deprecated. Prefer the jobs-namespace cancel endpoints: POST /api/jobs/cancel for cancelling jobs by ID, and POST /api/jobs/{job_id}/cancel for a single job.

Cancel specific jobs by ID (the delete field) or clear all pending jobs in the queue (the clear field). Despite the delete naming, this does not delete anything — listed jobs transition to the cancelled state, and delete cancels both pending and running jobs (not pending-only as previously documented). Job-by-ID cancellation is superseded by POST /api/jobs/cancel; clear has no jobs-namespace replacement yet.