feat: Add Shipping API controller

Created backend API for fetching WooCommerce shipping zones.

New Files:
- includes/Api/ShippingController.php

Features:
✅ GET /settings/shipping/zones endpoint
✅ Fetches all WooCommerce shipping zones
✅ Includes shipping methods for each zone
✅ Handles "Rest of the World" zone (zone 0)
✅ Returns formatted region names
✅ Returns method costs (Free, Calculated, or price)
✅ Permission check: manage_woocommerce

Data Structure:
- id: Zone ID
- name: Zone name
- order: Display order
- regions: Comma-separated region names
- rates: Array of shipping methods
  - id: Method instance ID
  - name: Method title
  - price: Formatted price or "Free"/"Calculated"
  - enabled: Boolean

Integration:
- Registered in Routes.php
- Uses WC_Shipping_Zones API
- Compatible with all WooCommerce shipping methods

includes/Api/Routes.php

@@ -9,6 +9,7 @@ use WooNooW\Api\AnalyticsController;
 use WooNooW\Api\AuthController;
 use WooNooW\API\PaymentsController;
 use WooNooW\API\StoreController;
+use WooNooW\Api\ShippingController;
 
 class Routes {
     public static function init() {
@@ -49,6 +50,10 @@ class Routes {
             // Store controller
             $store_controller = new StoreController();
             $store_controller->register_routes();
+            
+            // Shipping controller
+            $shipping_controller = new ShippingController();
+            $shipping_controller->register_routes();
         });
     }
 }