Stats Queue Endpoint

Public-safe preview of the live in-flight queue for the /statistics page.

Returns the top limit jobs in worker-processing order (running first, then pending FIFO), each with its position, size, ETA, and display metadata — but none of the identifying fields the admin /queue exposes (no user_id, raw URL, or job_id). count is the full queue length so the UI can show "+ N more". Cached ~10s, so it's near-live without hammering Postgres.