Call hydrogen's storefront.graphql directly, drop the compat shim

Completes the migration started in f8c3ef9. That commit put hydrogen
underneath the existing shopifyFetch wrapper; this one removes the
wrapper so every query uses the package's own client API.

- All 22 call sites now call storefront.graphql(DOCUMENT, { variables })
  (cachedStorefront for shop policies) instead of shopifyFetch, which
  emulated the old client's {query, variables} -> {data} shape.
- shopifyFetch is replaced by unwrapStorefrontResult(result, operation),
  which is only an error policy, not a transport wrapper: it returns
  data and throws when Shopify reports GraphQL errors, since hydrogen
  returns those rather than throwing. Naming the operation means a
  failure points at the call site instead of just at "Shopify".
- Environment reads move to services/shopify/config, so client.ts is
  only the hydrogen clients and shop-pay-button no longer imports from
  a query module just to get the store domain.
- Removes @shopify/storefront-api-client, the superseded client. It had
  no importers.

The SHOPIFY_STOREFRONT_API_URL export is gone too — hydrogen builds the
endpoint from storeDomain and apiVersion, and nothing else used it.

No behaviour change intended: same documents, same env var names, same
2025-07 API pin, same caching split between the two clients.

yarn typecheck passes with 0 errors. Verified against mock.shop: build
prerenders the policy pages, and in the browser product grid, search,
collection filters, cart restore, quantity update and discount-code
apply all work with no console errors. Customer account flows remain
untested — they need real credentials.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JaxgqPbFxLsSuLPZom2kdC

hooks/use-shopify-cart.ts

@@ -1,7 +1,7 @@
 'use client';
 
 import { create } from 'zustand';
-import { shopifyFetch } from '@/services/shopify/client';
+import { storefront, unwrapStorefrontResult } from '@/services/shopify/client';
 import {
   CREATE_CART_MUTATION,
   ADD_CART_LINES_MUTATION,
@@ -119,69 +119,79 @@ function unwrapCartPayload<T>(
 }
 
 async function createCartApi(lines: CartLineInput[] = []): Promise<Cart> {
-  const response = await shopifyFetch({
-    query: CREATE_CART_MUTATION,
-    variables: { lines: lines.length > 0 ? lines : null },
-  });
+  const data = unwrapStorefrontResult(
+    await storefront.graphql(CREATE_CART_MUTATION, {
+      variables: { lines: lines.length > 0 ? lines : null },
+    }),
+    'CreateCart'
+  );
 
-  return unwrapCartPayload(response.data.cartCreate);
+  return unwrapCartPayload(data.cartCreate);
 }
 
 async function addCartLinesApi(
   cartId: string,
   lines: CartLineInput[]
 ): Promise<Cart> {
-  const response = await shopifyFetch({
-    query: ADD_CART_LINES_MUTATION,
-    variables: { cartId, lines },
-  });
+  const data = unwrapStorefrontResult(
+    await storefront.graphql(ADD_CART_LINES_MUTATION, {
+      variables: { cartId, lines },
+    }),
+    'AddCartLines'
+  );
 
-  return unwrapCartPayload(response.data.cartLinesAdd);
+  return unwrapCartPayload(data.cartLinesAdd);
 }
 
 async function updateCartLinesApi(
   cartId: string,
   lines: CartLineUpdateInput[]
 ): Promise<Cart> {
-  const response = await shopifyFetch({
-    query: UPDATE_CART_LINES_MUTATION,
-    variables: { cartId, lines },
-  });
+  const data = unwrapStorefrontResult(
+    await storefront.graphql(UPDATE_CART_LINES_MUTATION, {
+      variables: { cartId, lines },
+    }),
+    'UpdateCartLines'
+  );
 
-  return unwrapCartPayload(response.data.cartLinesUpdate);
+  return unwrapCartPayload(data.cartLinesUpdate);
 }
 
 async function removeCartLinesApi(
   cartId: string,
   lineIds: string[]
 ): Promise<Cart> {
-  const response = await shopifyFetch({
-    query: REMOVE_CART_LINES_MUTATION,
-    variables: { cartId, lineIds },
-  });
+  const data = unwrapStorefrontResult(
+    await storefront.graphql(REMOVE_CART_LINES_MUTATION, {
+      variables: { cartId, lineIds },
+    }),
+    'RemoveCartLines'
+  );
 
-  return unwrapCartPayload(response.data.cartLinesRemove);
+  return unwrapCartPayload(data.cartLinesRemove);
 }
 
 async function updateCartDiscountCodesApi(
   cartId: string,
   discountCodes: string[]
 ): Promise<Cart> {
-  const response = await shopifyFetch({
-    query: UPDATE_CART_DISCOUNT_CODES_MUTATION,
-    variables: { cartId, discountCodes },
-  });
+  const data = unwrapStorefrontResult(
+    await storefront.graphql(UPDATE_CART_DISCOUNT_CODES_MUTATION, {
+      variables: { cartId, discountCodes },
+    }),
+    'UpdateCartDiscountCodes'
+  );
 
-  return unwrapCartPayload(response.data.cartDiscountCodesUpdate);
+  return unwrapCartPayload(data.cartDiscountCodesUpdate);
 }
 
 async function getCartApi(cartId: string): Promise<Cart | null> {
-  const response = await shopifyFetch({
-    query: GET_CART_QUERY,
-    variables: { cartId },
-  });
+  const data = unwrapStorefrontResult(
+    await storefront.graphql(GET_CART_QUERY, { variables: { cartId } }),
+    'GetCart'
+  );
 
-  return response.data.cart;
+  return data.cart;
 }
 
 export function redirectToCheckout(checkoutUrl: string): void {