fix: prevent asset conflicts between React and Grid.js versions

Add coexistence checks to all enqueue methods to prevent loading
both React and Grid.js assets simultaneously.

Changes:
- ReactAdmin.php: Only enqueue React assets when ?react=1
- Init.php: Skip Grid.js when React active on admin pages
- Form.php, Coupon.php, Access.php: Restore classic assets when ?react=0
- Customer.php, Product.php, License.php: Add coexistence checks

Now the toggle between Classic and React versions works correctly.

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

includes/Product.php

@@ -106,10 +106,13 @@ class Product {
     }
 
     public function enqueue_admin() {
-        // Assets now handled by ReactAdmin class
-        return;
-
         global $current_screen;
+
+        // Check coexistence mode - if React is active, don't load classic assets
+        $use_react = isset($_GET['react']) || get_option('formipay_use_react_admin', false);
+        if ($use_react) {
+            return;
+        }
         
         if($current_screen->id == 'formipay_page_formipay-products') {