Create packing slip

Generate a packing slip document for an order.

Use this endpoint right before packing/dispatch to produce a printable artifact.

Input behavior:

• Accepts optional format query parameter.
• Supports document output in pdf or csv depending on request format.

Rules:

• Order must belong to the authenticated seller.
• Returns 404 when the order cannot be found.

Response:

• Returns generated document bytes with a format-appropriate content type.