Replace @shopify/hydrogen with direct Storefront API queries

Vercel's 'Hydrogen (v1)' preset matches any project depending on
@shopify/hydrogen and runs its v1 builder, which fails looking for
dist/worker. We only used the preview package as a Storefront API client,
so talk to the API directly instead:

- services/shopify/client.ts: plain fetch to /api/{version}/graphql.json
  with the public token header, @inContext country/language defaults, and
  the same graphql() / unwrapStorefrontResult API as before
- graphql/gql.ts: small helper that joins a document with its fragments
  (de-duplicated); the queries themselves are unchanged
- Explicit response types at each call site in place of the generated
  gql.tada types; local ProductFilter input type
- Drop @shopify/hydrogen, graphql, the TS plugin and 'hydrogen gql check'
- Copy no longer mentions Hydrogen

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/services/shopify/customer.ts

@@ -80,6 +80,15 @@ export interface AuthResult {
   errors: CustomerUserError[];
 }
 
+// Payload shapes the customer mutations select. Shopify returns a null payload
+// when a mutation could not run at all.
+interface UserErrorsPayload {
+  customerUserErrors: CustomerUserError[] | null;
+}
+type TokenPayload = UserErrorsPayload & {
+  customerAccessToken: AccessToken | null;
+};
+
 const firstMessage = (errors: CustomerUserError[]) =>
   errors[0]?.message ?? 'Something went wrong. Please try again.';
 
@@ -100,9 +109,10 @@ export async function createCustomer(input: {
   acceptsMarketing?: boolean;
 }): Promise<{ errors: CustomerUserError[] }> {
   const data = unwrapStorefrontResult(
-    await storefront.graphql(CUSTOMER_CREATE_MUTATION, {
-      variables: { input },
-    }),
+    await storefront.graphql<{ customerCreate: UserErrorsPayload | null }>(
+      CUSTOMER_CREATE_MUTATION,
+      { variables: { input } }
+    ),
     'CustomerCreate'
   );
 
@@ -117,9 +127,10 @@ export async function login(
   password: string
 ): Promise<AuthResult> {
   const data = unwrapStorefrontResult(
-    await storefront.graphql(CUSTOMER_ACCESS_TOKEN_CREATE_MUTATION, {
-      variables: { input: { email, password } },
-    }),
+    await storefront.graphql<{ customerAccessTokenCreate: TokenPayload | null }>(
+      CUSTOMER_ACCESS_TOKEN_CREATE_MUTATION,
+      { variables: { input: { email, password } } }
+    ),
     'CustomerAccessTokenCreate'
   );
 
@@ -161,9 +172,10 @@ export async function resetPassword(
   password: string
 ): Promise<AuthResult> {
   const data = unwrapStorefrontResult(
-    await storefront.graphql(CUSTOMER_RESET_MUTATION, {
-      variables: { id, input: { resetToken, password } },
-    }),
+    await storefront.graphql<{ customerReset: TokenPayload | null }>(
+      CUSTOMER_RESET_MUTATION,
+      { variables: { id, input: { resetToken, password } } }
+    ),
     'CustomerReset'
   );
 
@@ -182,9 +194,10 @@ export async function activateAccount(
   password: string
 ): Promise<AuthResult> {
   const data = unwrapStorefrontResult(
-    await storefront.graphql(CUSTOMER_ACTIVATE_MUTATION, {
-      variables: { id, input: { activationToken, password } },
-    }),
+    await storefront.graphql<{ customerActivate: TokenPayload | null }>(
+      CUSTOMER_ACTIVATE_MUTATION,
+      { variables: { id, input: { activationToken, password } } }
+    ),
     'CustomerActivate'
   );
 
@@ -203,7 +216,7 @@ export async function getCustomer(
 ): Promise<Customer | null> {
   try {
     const data = unwrapStorefrontResult(
-      await storefront.graphql(CUSTOMER_QUERY, {
+      await storefront.graphql<{ customer: Customer | null }>(CUSTOMER_QUERY, {
         variables: { customerAccessToken: accessToken, orderCount },
       }),
       'GetCustomer'
@@ -227,7 +240,9 @@ export async function updateCustomer(
   }
 ): Promise<{ customer: Customer | null; errors: CustomerUserError[] }> {
   const data = unwrapStorefrontResult(
-    await storefront.graphql(CUSTOMER_UPDATE_MUTATION, {
+    await storefront.graphql<{
+      customerUpdate: (UserErrorsPayload & { customer: Customer | null }) | null;
+    }>(CUSTOMER_UPDATE_MUTATION, {
       variables: { customerAccessToken: accessToken, customer },
     }),
     'CustomerUpdate'