Renew Domain

Renew a domain for 1 additional year. Creates a Stripe checkout session for the renewal payment. The user must open the checkout URL to complete payment, after which the domain will be renewed automatically via the registrar. The order must be in "complete" status (i.e., the domain was previously registered successfully). Args: order_id: The order ID of a completed domain purchase (e.g. "ord_abc123"). Returns: Dict with order_id, checkout_url, price_cents, price_display, domain, and renewal_years.