Prism Location Resolutions

Available location grains for an insight + entity set, as the Prism service account would see them (same access rules as refresh).

The grains returned are exactly those get_framework_filters reports for daily grain — no fabricated fallback. An insight can advertise day support in the ontology yet have no daily table for a given entity/location slice, so surfacing a grain that doesn't exist only dead-ends later at purchase with "no tables found". When nothing is available, options is empty and default is null; CAMS blocks the save rather than offering a grain that can't be computed.