fix: Improve shipping toggle and simplify UI

Fixed toggle functionality and cleaned up redundant buttons.

Backend Fix:
✅ Fixed toggle to properly update shipping method settings
✅ Get existing settings, update enabled field, save back
✅ Previously was trying to save wrong data structure

Frontend Changes:
✅ Removed "View in WooCommerce" from header (redundant)
✅ Changed "Edit zone" to "Settings" button (prepares for modal)
✅ Changed "+ Add shipping zone" to "Manage Zones in WooCommerce"
✅ Added modal state (selectedZone, isModalOpen)
✅ Added Dialog/Drawer imports for future modal implementation

Button Strategy:
- Header: Refresh only
- Zone card: Settings button (will open modal)
- Bottom: "Manage Zones in WooCommerce" (for add/edit/delete zones)

Next Step:
Implement settings modal similar to Payments page with zone/method configuration

includes/Api/ShippingController.php

@@ -210,8 +210,9 @@ class ShippingController extends WP_REST_Controller {
 					$method_found = true;
 					
 					// Update the enabled status
-					$method->enabled = $enabled ? 'yes' : 'no';
-					update_option( $method->get_instance_option_key(), $method->instance_settings );
+					$settings = get_option( $method->get_instance_option_key(), array() );
+					$settings['enabled'] = $enabled ? 'yes' : 'no';
+					update_option( $method->get_instance_option_key(), $settings );
 					
 					break;
 				}