Lock an order

Lock the order to prevent further edits. Once locked, the order's items, payments and other sub-resources reject mutation attempts with 403 Forbidden. Used to freeze an order during a settlement, audit or close-of-day process; pair with POST /shop/orders/{orderId}/unlock to release the lock.

The action is idempotent — locking an already-locked order returns the same response without error. Records a locked audit-log entry against the order.