Redesign cart and collections, fix product pagination

- Cart drawer: single-column layout matching the site — no bag icon,
  no dividers, square images, tighter type, discount code form,
  estimated total, and a Go to Checkout button
- Cart: per-line loading state so one row's update no longer disables
  every other row or the checkout button
- Discounts: cartDiscountCodesUpdate mutation plus discountCodes on the
  cart fragment, wired to an applyDiscountCode store action
- Products: fix "load more" returning the same first page — the query
  now takes an `after` cursor and getProductsPage exposes pageInfo
- Collections: cards match the product cards (no border, radius, blurb,
  or CTA row) at 4-up on desktop and 2-up on mobile; section headers
  match the products section
- Shop Pay: cart permalink with payment=shop_pay instead of the hosted
  shop-js element
- Buttons converted to the shadcn Button component throughout
- PDP: swipeable image carousel with dots on mobile, sticky info column,
  colour swatches never fall back to variant photos
- Rename the store from Stride to Shop; larger header wordmark

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016jWbNNJLksC1QG8z8845FX

app/page.tsx

@@ -6,7 +6,7 @@ export default function Page() {
   return (
     <>
       <Header
-        storeName="Stride"
+        storeName="Shop"
         logoUrl=""
         links={[
           { label: 'Products', url: '/' },
@@ -18,8 +18,8 @@ export default function Page() {
         subtitle="An agent-friendly Shopify storefront built with Next.js and Hydrogen."
       />
       <Footer
-        storeName="Stride"
-        copyright="© 2026 Stride. All rights reserved."
+        storeName="Shop"
+        copyright="© 2026 Shop. All rights reserved."
       />
     </>
   );