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- Removes @shopify/storefront-api-client, the superseded client.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-policies.ts

@@ -1,4 +1,7 @@
-import { shopifyFetch } from '@/services/shopify/client';
+import {
+  cachedStorefront,
+  unwrapStorefrontResult,
+} from '@/services/shopify/client';
 import { GET_SHOP_POLICIES_QUERY } from '@/graphql/policies';
 
 export interface ShopPolicy {
@@ -22,12 +25,12 @@ export const POLICY_HANDLES = [
 // hourly) rather than the no-store one used for carts and products.
 export async function getShopPolicies(): Promise<ShopPolicy[]> {
   try {
-    const { data } = await shopifyFetch({
-      query: GET_SHOP_POLICIES_QUERY,
-      cache: true,
-    });
+    const data = unwrapStorefrontResult(
+      await cachedStorefront.graphql(GET_SHOP_POLICIES_QUERY),
+      'GetShopPolicies'
+    );
 
-    return Object.values(data?.shop ?? {}).filter(
+    return Object.values(data.shop ?? {}).filter(
       (policy): policy is ShopPolicy => Boolean(policy?.handle)
     );
   } catch (err) {