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/mutations/Checkout.ts

@@ -0,0 +1,154 @@
+import { gql } from "@apollo/client";
+import { CHECKOUT_FRAGMENT } from "../fragments/Checkout";
+
+export const CHECKOUT_CREATE = gql`
+  mutation CheckoutCreate($input: CheckoutCreateInput!) {
+    checkoutCreate(input: $input) {
+      checkout {
+        ...CheckoutFragment
+      }
+      errors {
+        field
+        message
+        code
+      }
+    }
+  }
+  ${CHECKOUT_FRAGMENT}
+`;
+
+export const CHECKOUT_LINES_ADD = gql`
+  mutation CheckoutLinesAdd($checkoutId: ID!, $lines: [CheckoutLineInput!]!) {
+    checkoutLinesAdd(checkoutId: $checkoutId, lines: $lines) {
+      checkout {
+        ...CheckoutFragment
+      }
+      errors {
+        field
+        message
+        code
+      }
+    }
+  }
+  ${CHECKOUT_FRAGMENT}
+`;
+
+export const CHECKOUT_LINES_UPDATE = gql`
+  mutation CheckoutLinesUpdate($checkoutId: ID!, $lines: [CheckoutLineUpdateInput!]!) {
+    checkoutLinesUpdate(checkoutId: $checkoutId, lines: $lines) {
+      checkout {
+        ...CheckoutFragment
+      }
+      errors {
+        field
+        message
+        code
+      }
+    }
+  }
+  ${CHECKOUT_FRAGMENT}
+`;
+
+export const CHECKOUT_LINES_DELETE = gql`
+  mutation CheckoutLinesDelete($checkoutId: ID!, $lineIds: [ID!]!) {
+    checkoutLinesDelete(checkoutId: $checkoutId, lines: $lineIds) {
+      checkout {
+        ...CheckoutFragment
+      }
+      errors {
+        field
+        message
+        code
+      }
+    }
+  }
+  ${CHECKOUT_FRAGMENT}
+`;
+
+export const CHECKOUT_SHIPPING_ADDRESS_UPDATE = gql`
+  mutation CheckoutShippingAddressUpdate($checkoutId: ID!, $shippingAddress: AddressInput!) {
+    checkoutShippingAddressUpdate(checkoutId: $checkoutId, shippingAddress: $shippingAddress) {
+      checkout {
+        ...CheckoutFragment
+      }
+      errors {
+        field
+        message
+        code
+      }
+    }
+  }
+  ${CHECKOUT_FRAGMENT}
+`;
+
+export const CHECKOUT_BILLING_ADDRESS_UPDATE = gql`
+  mutation CheckoutBillingAddressUpdate($checkoutId: ID!, $billingAddress: AddressInput!) {
+    checkoutBillingAddressUpdate(checkoutId: $checkoutId, billingAddress: $billingAddress) {
+      checkout {
+        ...CheckoutFragment
+      }
+      errors {
+        field
+        message
+        code
+      }
+    }
+  }
+  ${CHECKOUT_FRAGMENT}
+`;
+
+export const CHECKOUT_SHIPPING_METHOD_UPDATE = gql`
+  mutation CheckoutShippingMethodUpdate($checkoutId: ID!, $shippingMethodId: ID!) {
+    checkoutShippingMethodUpdate(checkoutId: $checkoutId, shippingMethodId: $shippingMethodId) {
+      checkout {
+        ...CheckoutFragment
+      }
+      errors {
+        field
+        message
+        code
+      }
+    }
+  }
+  ${CHECKOUT_FRAGMENT}
+`;
+
+export const CHECKOUT_COMPLETE = gql`
+  mutation CheckoutComplete($checkoutId: ID!) {
+    checkoutComplete(checkoutId: $checkoutId) {
+      order {
+        id
+        number
+        status
+        created
+        total {
+          gross {
+            amount
+            currency
+          }
+        }
+      }
+      errors {
+        field
+        message
+        code
+      }
+    }
+  }
+`;
+
+export const CHECKOUT_EMAIL_UPDATE = gql`
+  mutation CheckoutEmailUpdate($checkoutId: ID!, $email: String!) {
+    checkoutEmailUpdate(checkoutId: $checkoutId, email: $email) {
+      checkout {
+        ...CheckoutFragment
+      }
+      errors {
+        field
+        message
+        code
+      }
+    }
+  }
+  ${CHECKOUT_FRAGMENT}
+`;