Side-loaded entity data for shipment search responses.

Each shipment references its parent procurement by ID; resolve it here. Procurements are shallow — their own item entities are not surfaced — but the organisations and businesses they reference (buyer/supplier/work provider) are included so callers can resolve the shipment's parties.

A shipment as surfaced by the search/list APIs. The sender/receiver organisations and shipping price are resolved from the parent procurement (via the procurements and organizations entities maps), not duplicated here.