RFQ
RFQ-first booking: create an open RFQ, read stored shipper-facing quotes, then accept a quote by quoteId to create the shipment.
Create an RFQ
**Purpose (Flow C, step 1):** Create an open RFQ from a shipment payload **without** creating a shipment.
Get quotes for an RFQ
**Purpose (Flow C, step 2):** Return quotes already stored for an existing RFQ owned by the authenticated shipper.
Accept an RFQ quote and create shipment
**Purpose (Flow C, step 3):** Accept a stored RFQ quote and create the shipment.