Hand a batch of orders to one staff member.

One target for the whole batch, by design: the POS asks for the new server
once and applies it to everything selected, so there is no per-order choice
to encode. Transferring two orders to two different people is two requests.

The batch is capped because it is applied in one transaction and the UI
selects from a visible list — a request naming thousands of orders is not a
floor action, and the cap keeps one from holding row locks across the whole
table.