fix(dashboard): honor order options.incoterm in createShipmentFromOrders

[DarkSwoop]

Problem

createShipmentFromOrders (packages/lib/helper.ts) derives the customs incoterm
solely from the freight payer:

incoterm: payment?.paid_by == "sender" ? "DDP" : "DDU",

Since paid_by defaults to sender, every shipment built from an order is forced
to DDP, and there is no way to request a different term of trade through the
order's options.

Impact (dhl_express)

Freight payer and terms of trade are independent at the carrier level — dhl_express
maps payment.paid_by → ShippingPaymentType and customs.incoterm → TermsOfTrade
separately. Coupling them in the dashboard means a sender-paid DHL shipment can never
be DDU: the recipient can't be made to pay duties while freight stays billed to the
sender.

Fix

Honor an explicit options.incoterm from the order, normalized and validated against
the INCOTERMS enum; fall back to the existing paid_by-derived default when absent
or invalid:

const order_incoterm = `${order_options.incoterm || ""}`.toUpperCase();
const incoterm =
  (INCOTERMS.includes(order_incoterm) ? order_incoterm : null) ||
  (payment?.paid_by == "sender" ? "DDP" : "DDU");

Now possible: an order with options.incoterm = "DDU" produces a DHL label with
TermsOfTrade=DDU while freight stays billed to the sender (ShippingPaymentType=S).
Additive change — orders without options.incoterm behave exactly as before, and the
value remains a pre-fill users can still edit in the customs form.

[vercel]

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