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()

includes/Api/CheckoutController.php

@@ -414,11 +414,6 @@ class CheckoutController {
         }
 
         // Shipping (best‑effort estimate)
-        // DEBUG: Log shipping data for troubleshooting
-        error_log('[WooNooW Shipping Debug] shipping_method: ' . ($payload['shipping_method'] ?? 'null'));
-        error_log('[WooNooW Shipping Debug] shipping_cost: ' . ($payload['shipping_cost'] ?? 'null'));
-        error_log('[WooNooW Shipping Debug] shipping_title: ' . ($payload['shipping_title'] ?? 'null'));
-        
         if (!empty($payload['shipping_method'])) {
             $rate = $this->find_shipping_rate_for_order($order, $payload['shipping_method']);
             if ($rate instanceof WC_Shipping_Rate) {
@@ -431,7 +426,6 @@ class CheckoutController {
                     'taxes'        => $rate->get_taxes(),
                 ]);
                 $order->add_item($item);
-                error_log('[WooNooW Shipping Debug] Added shipping via WC rate lookup: ' . $rate->get_cost());
             } elseif (!empty($payload['shipping_cost']) && $payload['shipping_cost'] > 0) {
                 // Fallback: use shipping_cost directly from frontend
                 // This handles API-based shipping like Rajaongkir where WC zones don't apply
@@ -449,9 +443,6 @@ class CheckoutController {
                     'total'        => floatval($payload['shipping_cost']),
                 ]);
                 $order->add_item($item);
-                error_log('[WooNooW Shipping Debug] Added shipping via frontend fallback: ' . $payload['shipping_cost']);
-            } else {
-                error_log('[WooNooW Shipping Debug] NO shipping added - rate lookup failed and no valid shipping_cost');
             }
         }
 
@@ -571,9 +562,10 @@ class CheckoutController {
 
     /**
      * Get list of standard WooCommerce field keys
+     * Plugins can extend this list via the 'woonoow_standard_checkout_field_keys' filter
      */
     private function get_standard_field_keys(): array {
-        return [
+        $keys = [
             'billing_first_name',
             'billing_last_name',
             'billing_company',
@@ -596,6 +588,14 @@ class CheckoutController {
             'shipping_postcode',
             'order_comments',
         ];
+        
+        /**
+         * Filter the list of standard checkout field keys.
+         * Plugins can add their own field keys to be recognized as "standard" (not custom).
+         *
+         * @param array $keys List of standard field keys
+         */
+        return apply_filters('woonoow_standard_checkout_field_keys', $keys);
     }
 
     /** ----------------- Helpers ----------------- **/