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/queries/Checkout.ts

@@ -0,0 +1,21 @@
+import { gql } from "@apollo/client";
+import { CHECKOUT_FRAGMENT } from "../fragments/Checkout";
+
+export const GET_CHECKOUT = gql`
+  query GetCheckout($token: UUID!) {
+    checkout(token: $token) {
+      ...CheckoutFragment
+    }
+  }
+  ${CHECKOUT_FRAGMENT}
+`;
+
+export const GET_CHECKOUT_BY_ID = gql`
+  query GetCheckoutById($id: ID!) {
+    checkout(id: $id) {
+      ...CheckoutFragment
+    }
+  }
+  ${CHECKOUT_FRAGMENT}
+`;
+`;

src/lib/saleor/queries/Products.ts

@@ -0,0 +1,51 @@
+import { gql } from "@apollo/client";
+import { PRODUCT_FRAGMENT, PRODUCT_LIST_ITEM_FRAGMENT } from "../fragments/Product";
+
+export const GET_PRODUCTS = gql`
+  query GetProducts($channel: String!, $locale: LanguageCodeEnum!, $first: Int!) {
+    products(channel: $channel, first: $first) {
+      edges {
+        node {
+          ...ProductListItemFragment
+        }
+      }
+      pageInfo {
+        hasNextPage
+        endCursor
+      }
+    }
+  }
+  ${PRODUCT_LIST_ITEM_FRAGMENT}
+`;
+
+export const GET_PRODUCT_BY_SLUG = gql`
+  query GetProduct($slug: String!, $channel: String!, $locale: LanguageCodeEnum!) {
+    product(slug: $slug, channel: $channel) {
+      ...ProductFragment
+    }
+  }
+  ${PRODUCT_FRAGMENT}
+`;
+
+export const GET_PRODUCTS_BY_CATEGORY = gql`
+  query GetProductsByCategory(
+    $categorySlug: String!
+    $channel: String!
+    $locale: LanguageCodeEnum!
+    $first: Int!
+  ) {
+    category(slug: $categorySlug) {
+      id
+      name
+      slug
+      products(channel: $channel, first: $first) {
+        edges {
+          node {
+            ...ProductListItemFragment
+          }
+        }
+      }
+    }
+  }
+  ${PRODUCT_LIST_ITEM_FRAGMENT}
+`;