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/delegate/src/closest.js

@@ -0,0 +1,33 @@
+var DOCUMENT_NODE_TYPE = 9;
+
+/**
+ * A polyfill for Element.matches()
+ */
+if (typeof Element !== 'undefined' && !Element.prototype.matches) {
+    var proto = Element.prototype;
+
+    proto.matches = proto.matchesSelector ||
+                    proto.mozMatchesSelector ||
+                    proto.msMatchesSelector ||
+                    proto.oMatchesSelector ||
+                    proto.webkitMatchesSelector;
+}
+
+/**
+ * Finds the closest parent that matches a selector.
+ *
+ * @param {Element} element
+ * @param {String} selector
+ * @return {Function}
+ */
+function closest (element, selector) {
+    while (element && element.nodeType !== DOCUMENT_NODE_TYPE) {
+        if (typeof element.matches === 'function' &&
+            element.matches(selector)) {
+          return element;
+        }
+        element = element.parentNode;
+    }
+}
+
+module.exports = closest;