feat(saleor): Phase 1 - GraphQL Client Setup

- Add Apollo Client for Saleor GraphQL API
- Create GraphQL fragments (Product, Variant, Checkout)
- Create GraphQL queries (Products, Checkout)
- Create GraphQL mutations (Checkout operations)
- Add TypeScript types for Saleor entities
- Add product helper functions
- Install @apollo/client and graphql dependencies

Part of WordPress/WooCommerce → Saleor migration

src/lib/saleor/index.ts

@@ -0,0 +1,35 @@
+// Saleor GraphQL Client and Utilities
+export { saleorClient } from "./client";
+
+// Fragments
+export { PRODUCT_FRAGMENT, PRODUCT_LIST_ITEM_FRAGMENT } from "./fragments/Product";
+export { PRODUCT_VARIANT_FRAGMENT, CHECKOUT_LINE_FRAGMENT } from "./fragments/Variant";
+export { CHECKOUT_FRAGMENT, ADDRESS_FRAGMENT } from "./fragments/Checkout";
+
+// Queries
+export { GET_PRODUCTS, GET_PRODUCT_BY_SLUG, GET_PRODUCTS_BY_CATEGORY } from "./queries/Products";
+export { GET_CHECKOUT, GET_CHECKOUT_BY_ID } from "./queries/Checkout";
+
+// Mutations
+export {
+  CHECKOUT_CREATE,
+  CHECKOUT_LINES_ADD,
+  CHECKOUT_LINES_UPDATE,
+  CHECKOUT_LINES_DELETE,
+  CHECKOUT_SHIPPING_ADDRESS_UPDATE,
+  CHECKOUT_BILLING_ADDRESS_UPDATE,
+  CHECKOUT_SHIPPING_METHOD_UPDATE,
+  CHECKOUT_COMPLETE,
+  CHECKOUT_EMAIL_UPDATE,
+} from "./mutations/Checkout";
+
+// Helper functions
+export {
+  getProducts,
+  getProductBySlug,
+  getProductPrice,
+  getProductImage,
+  isProductAvailable,
+  formatPrice,
+  getLocalizedProduct,
+} from "./products";