Contribute button now offers "Pay Now" (creates a PaymentRequest linked
to the cart, navigates to the existing payment page) alongside "Record
Manual". When the payment completes, the server auto-records a
contribution on the cart with amount, method, and txHash.
- Add recipientAddress to ShoppingCartDoc, linkedCartId to PaymentRequestMeta
- New POST /api/shopping-carts/:cartId/contribute-pay route
- Payment status handler propagates paid → cart contribution
- Payment page shows "Return to Cart" link for linked payments
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>