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

hooks/use-shopify-cart.ts

@@ -7,6 +7,7 @@ import {
   ADD_CART_LINES_MUTATION,
   UPDATE_CART_LINES_MUTATION,
   REMOVE_CART_LINES_MUTATION,
+  UPDATE_CART_DISCOUNT_CODES_MUTATION,
   GET_CART_QUERY,
 } from '@/graphql/cart';
 import { useEffect } from 'react';
@@ -59,10 +60,16 @@ interface CartLine {
   };
 }
 
+export interface CartDiscountCode {
+  code: string;
+  applicable: boolean;
+}
+
 export interface Cart {
   id: string;
   checkoutUrl: string;
   totalQuantity: number;
+  discountCodes?: CartDiscountCode[];
   cost: {
     subtotalAmount: {
       amount: string;
@@ -147,6 +154,24 @@ async function removeCartLinesApi(
   return response.data.cartLinesRemove.cart;
 }
 
+async function updateCartDiscountCodesApi(
+  cartId: string,
+  discountCodes: string[]
+): Promise<Cart> {
+  const response = await shopifyFetch({
+    query: UPDATE_CART_DISCOUNT_CODES_MUTATION,
+    variables: { cartId, discountCodes },
+  });
+
+  if (response.data.cartDiscountCodesUpdate.userErrors.length > 0) {
+    throw new Error(
+      response.data.cartDiscountCodesUpdate.userErrors[0].message
+    );
+  }
+
+  return response.data.cartDiscountCodesUpdate.cart;
+}
+
 async function getCartApi(cartId: string): Promise<Cart | null> {
   const response = await shopifyFetch({
     query: GET_CART_QUERY,
@@ -186,6 +211,7 @@ interface CartState {
   addItem: (variantId: string, quantity?: number) => Promise<Cart>;
   removeItem: (lineId: string) => Promise<Cart>;
   updateItemQuantity: (lineId: string, quantity: number) => Promise<Cart>;
+  applyDiscountCode: (code: string) => Promise<Cart>;
   refreshCart: () => Promise<void>;
 }
 
@@ -312,6 +338,29 @@ export const useCartStore = create<CartState>((set, get) => ({
     }
   },
 
+  // Apply a discount code. Shopify accepts unknown codes and reports them back
+  // as `applicable: false`, so callers should check the returned cart.
+  applyDiscountCode: async (code: string) => {
+    const { cartId } = get();
+    if (!cartId) throw new Error('No cart exists');
+
+    try {
+      set({ loading: true, error: null });
+      const trimmed = code.trim();
+      const updatedCart = await updateCartDiscountCodesApi(
+        cartId,
+        trimmed ? [trimmed] : []
+      );
+      set({ cart: updatedCart, loading: false });
+      return updatedCart;
+    } catch (err) {
+      const errorMessage =
+        err instanceof Error ? err.message : 'Failed to apply discount code';
+      set({ error: errorMessage, loading: false });
+      throw err;
+    }
+  },
+
   // Refresh cart from Shopify
   refreshCart: async () => {
     const storedCartId = localStorage.getItem(CART_ID_KEY);
@@ -374,6 +423,7 @@ export function useShopifyCart() {
     addItem: store.addItem,
     removeItem: store.removeItem,
     updateItemQuantity: store.updateItemQuantity,
+    applyDiscountCode: store.applyDiscountCode,
     refreshCart: store.refreshCart,
   };
 }