fix: Add SALEOR_API_TOKEN auth for COD transaction creation

- Add SALEOR_API_TOKEN environment variable support
- Update Apollo client to include auth header
- Enable COD transaction creation after checkout

src/stores/saleorCheckoutStore.ts

@@ -75,6 +75,7 @@ interface SaleorCheckoutStore {
   openCart: () => void;
   closeCart: () => void;
   clearError: () => void;
+  clearCheckout: () => void;
 
   // Getters
   getLineCount: () => number;
@@ -299,6 +300,7 @@ export const useSaleorCheckoutStore = create<SaleorCheckoutStore>()(
       closeCart: () => set({ isOpen: false }),
       clearError: () => set({ error: null }),
       setLanguageCode: (languageCode: string) => set({ languageCode }),
+      clearCheckout: () => set({ checkout: null, checkoutToken: null }),
 
       getLineCount: () => {
         const { checkout } = get();