Get Available Fft Models

Models pre-cached on the caller's eligible PrimeClusters for FFT dispatch.

Same principal collapse as the dispatch picker (team wins when present, otherwise personal) and the same cluster filter (uncordoned

• heartbeat fresh + non-zero ClusterAllocation) so what surfaces here is what dispatch would actually land on. Only PRESENT-cache clusters contribute — ABSENT / ERROR would 400 the dispatch and NULL (unprobed) hasn't reported a manifest yet.

Each model carries the list of clusters it's warm on with gpu_type

• cache_synced_at so callers can pin the follow-up dispatch to a specific GPU family without hitting the "picker landed on a cluster that has the GPU but not this model" reject path.