Move Storefront queries onto @shopify/hydrogen preview client

Replaces the hand-rolled shopifyFetch wrapper and raw query strings with
the hydrogen preview package (0.0.0-preview-116d5d7-20260730141607), the
same build pinned in hydrogen-preview/.

- services/shopify/client: createStorefrontClient({type: "public"}) with a
  static request context. Two module-scoped clients — uncached for carts,
  products and customers; revalidate-3600 for shop policies — using the
  client's custom fetch option to carry Next's caching hints.
- graphql/*: every document wrapped in gql(), fragments composed via the
  second argument instead of string interpolation, and $country/$language
  declared with @inContext so hydrogen injects them.
- shopifyFetch keeps its {query, variables} call shape so call sites are
  unchanged, but is now generic over the document, so data is inferred. It
  re-raises GraphQL errors, which hydrogen returns rather than throws.

Env var names, the 2025-07 API version pin, and the client-side fetching
architecture are unchanged.

Turning on type coverage surfaced real defects, not just annotations:

- hydrogen gql check caught $discountCodes: [String!] used where the field
  requires [String!]!.
- Cart and customer mutation payloads are nullable and were dereferenced
  unconditionally, so a failed mutation threw a TypeError. Adds a shared
  unwrapCartPayload helper (collapsing five copies of the same userErrors
  check) and explicit null handling in the customer service, so a null
  payload reads as an error rather than success with no errors.
- Search results are a Product | Page | Article union; adds __typename to
  the queries and narrows on it.
- Widens nullable fields (altText, image, customer.email, totalTaxAmount)
  in the domain interfaces and in the structural duplicates some
  components declare locally.

Adds a typecheck script (tsc --noEmit && hydrogen gql check); it passes
with 0 errors. Two deprecation warnings are left alone as acting on them
would change behaviour: ProductOption.values and CartCost.totalTaxAmount.

Verified against mock.shop: build prerenders the policy pages through the
cached client, and in the browser the product grid, search with facets,
collection filter round-trip, add-to-cart and quantity update all work.
Customer account flows are untested — they need real credentials.

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

graphql/customer.ts

@@ -0,0 +1,178 @@
+// Customer account operations (classic Storefront customer accounts).
+// https://shopify.dev/docs/api/storefront/latest/objects/Customer
+import { gql } from '@shopify/hydrogen';
+
+const CustomerFragment = gql(`
+  fragment CustomerFragment on Customer {
+    id
+    email
+    firstName
+    lastName
+    phone
+    displayName
+    acceptsMarketing
+    createdAt
+    defaultAddress {
+      id
+      firstName
+      lastName
+      address1
+      address2
+      city
+      province
+      zip
+      country
+      phone
+    }
+  }
+`);
+
+export const CUSTOMER_QUERY = gql(
+  `
+  query GetCustomer($customerAccessToken: String!, $orderCount: Int!) {
+    customer(customerAccessToken: $customerAccessToken) {
+      ...CustomerFragment
+      orders(first: $orderCount, reverse: true) {
+        edges {
+          node {
+            id
+            orderNumber
+            processedAt
+            financialStatus
+            fulfillmentStatus
+            statusUrl
+            currentTotalPrice {
+              amount
+              currencyCode
+            }
+            lineItems(first: 5) {
+              edges {
+                node {
+                  title
+                  quantity
+                  variant {
+                    image {
+                      url
+                      altText
+                    }
+                  }
+                }
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+`,
+  [CustomerFragment]
+);
+
+export const CUSTOMER_CREATE_MUTATION = gql(`
+  mutation CustomerCreate($input: CustomerCreateInput!) {
+    customerCreate(input: $input) {
+      customer {
+        id
+        email
+      }
+      customerUserErrors {
+        code
+        field
+        message
+      }
+    }
+  }
+`);
+
+export const CUSTOMER_ACCESS_TOKEN_CREATE_MUTATION = gql(`
+  mutation CustomerAccessTokenCreate($input: CustomerAccessTokenCreateInput!) {
+    customerAccessTokenCreate(input: $input) {
+      customerAccessToken {
+        accessToken
+        expiresAt
+      }
+      customerUserErrors {
+        code
+        field
+        message
+      }
+    }
+  }
+`);
+
+export const CUSTOMER_ACCESS_TOKEN_DELETE_MUTATION = gql(`
+  mutation CustomerAccessTokenDelete($customerAccessToken: String!) {
+    customerAccessTokenDelete(customerAccessToken: $customerAccessToken) {
+      deletedAccessToken
+      userErrors {
+        field
+        message
+      }
+    }
+  }
+`);
+
+// Sends the "reset your password" email.
+export const CUSTOMER_RECOVER_MUTATION = gql(`
+  mutation CustomerRecover($email: String!) {
+    customerRecover(email: $email) {
+      customerUserErrors {
+        code
+        field
+        message
+      }
+    }
+  }
+`);
+
+// Completes the reset using the id + token from the emailed link.
+export const CUSTOMER_RESET_MUTATION = gql(`
+  mutation CustomerReset($id: ID!, $input: CustomerResetInput!) {
+    customerReset(id: $id, input: $input) {
+      customerAccessToken {
+        accessToken
+        expiresAt
+      }
+      customerUserErrors {
+        code
+        field
+        message
+      }
+    }
+  }
+`);
+
+// Activation link sent to customers created by the merchant.
+export const CUSTOMER_ACTIVATE_MUTATION = gql(`
+  mutation CustomerActivate($id: ID!, $input: CustomerActivateInput!) {
+    customerActivate(id: $id, input: $input) {
+      customerAccessToken {
+        accessToken
+        expiresAt
+      }
+      customerUserErrors {
+        code
+        field
+        message
+      }
+    }
+  }
+`);
+
+export const CUSTOMER_UPDATE_MUTATION = gql(
+  `
+  mutation CustomerUpdate($customerAccessToken: String!, $customer: CustomerUpdateInput!) {
+    customerUpdate(customerAccessToken: $customerAccessToken, customer: $customer) {
+      customer {
+        ...CustomerFragment
+      }
+      customerUserErrors {
+        code
+        field
+        message
+      }
+    }
+  }
+`,
+  [CustomerFragment]
+);