Update order

Apply a seller action to an order (for example shipping or dispute actions).

Use this endpoint to progress fulfillment or open item-level disputes from seller tools.

Behavior:

• Validates order ownership against the authenticated seller.
• Applies order-item updates through the shared order update engine.
• Supports structured action payloads (including shipment metadata when required).

Responses:

• Returns 204 on success.
• Returns 404 if the order cannot be found for the seller.