feat: cleanup and improvements for checkout fields

- Removed all debug logging (backend and frontend)
- Added filter hook 'woonoow_standard_checkout_field_keys' for extensibility
- Added form-row-wide class support to admin OrderForm
- Tax is automatically handled by WC's calculate_totals()

customer-spa/src/pages/Checkout/index.tsx

@@ -569,16 +569,6 @@ export default function Checkout() {
         custom_fields: customFieldData,
       };
 
-      // DEBUG: Log shipping data being sent
-      console.log('[WooNooW DEBUG] Order Shipping Data:', {
-        selectedShippingRate,
-        shippingCost,
-        shippingRatesCount: shippingRates.length,
-        foundRate: shippingRates.find(r => r.id === selectedShippingRate),
-        orderData_shipping_cost: orderData.shipping_cost,
-        orderData_shipping_title: orderData.shipping_title,
-      });
-
       // Submit order
       const response = await apiClient.post('/checkout/submit', orderData);
       const data = (response as any).data || response;