idle dashboard tabs do not spend claim or intelligence requests with no queued work

Prove the pipeline engine's frugality contract end-to-end in a real browser: the enrich stage calls /api/commute through the same-origin worker and a {locked:true} singleflight response does not crash the UI; and concurrent clients on the same workspace do NOT each fire the LLM/Maps calls because compute_lock holds the singleflight, with browsers self-selecting before CF Worker fallback claims.