Empty container returns now generate a downloadable Equipment Interchange Receipt: container number & size, exact return timestamp, depot/location, condition, and the carrier/booking reference. Customers can download it from their booking's Documents tab (own-booking returns only); staff can pull any via the same endpoint.
Empties had no way onto a departure: the return record could name a train
but nothing seated it on a wagon. Export schedules now expose a loading
action that packs selected returns onto free wagons at one 40ft or two 20ft
each, enforced both in the picker and in the API (existing empties on the
schedule count against their wagon).
Adds container_size, train_schedule_id and wagon_sequence_no to
freight.empty_container_returns.
