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>

node_modules/css-tree/cjs/utils/clone.cjs

@@ -0,0 +1,25 @@
+'use strict';
+
+const List = require('./List.cjs');
+
+function clone(node) {
+    const result = {};
+
+    for (const key in node) {
+        let value = node[key];
+
+        if (value) {
+            if (Array.isArray(value) || value instanceof List.List) {
+                value = value.map(clone);
+            } else if (value.constructor === Object) {
+                value = clone(value);
+            }
+        }
+
+        result[key] = value;
+    }
+
+    return result;
+}
+
+exports.clone = clone;