feat: Implement Payment Gateways backend foundation

✅ Phase 1 Backend Complete:

📦 PaymentGatewaysProvider.php:
- Read WC gateways from WC()->payment_gateways()
- Transform to clean JSON format
- Categorize: manual/provider/other
- Extract settings: basic/api/advanced
- Check requirements (SSL, extensions)
- Generate webhook URLs
- Respect WC bone structure (WC_Payment_Gateway)

📡 PaymentsController.php:
- GET /woonoow/v1/payments/gateways (list all)
- GET /woonoow/v1/payments/gateways/{id} (single)
- POST /woonoow/v1/payments/gateways/{id} (save settings)
- POST /woonoow/v1/payments/gateways/{id}/toggle (enable/disable)
- Permission checks (manage_woocommerce)
- Error handling with proper HTTP codes
- Response caching (5 min)

🔌 Integration:
- Registered in Api/Routes.php
- Auto-discovers all WC-compliant gateways
- No new hooks - listens to WC structure

📋 Checklist Progress:
- [x] PaymentGatewaysProvider.php
- [x] PaymentsController.php
- [x] REST API registration
- [ ] Frontend components (next)

includes/Api/Routes.php

@@ -7,6 +7,7 @@ use WooNooW\Api\CheckoutController;
 use WooNooW\Api\OrdersController;
 use WooNooW\Api\AnalyticsController;
 use WooNooW\Api\AuthController;
+use WooNooW\API\PaymentsController;
 
 class Routes {
     public static function init() {
@@ -39,6 +40,10 @@ class Routes {
             CheckoutController::register();
             OrdersController::register();
             AnalyticsController::register_routes();
+            
+            // Payments controller
+            $payments_controller = new PaymentsController();
+            $payments_controller->register_routes();
         });
     }
 }