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/core-js/modules/es.array-buffer.detached.js

@@ -0,0 +1,17 @@
+'use strict';
+var DESCRIPTORS = require('../internals/descriptors');
+var defineBuiltInAccessor = require('../internals/define-built-in-accessor');
+var isDetached = require('../internals/array-buffer-is-detached');
+
+var ArrayBufferPrototype = ArrayBuffer.prototype;
+
+// `ArrayBuffer.prototype.detached` getter
+// https://tc39.es/ecma262/#sec-get-arraybuffer.prototype.detached
+if (DESCRIPTORS && !('detached' in ArrayBufferPrototype)) {
+  defineBuiltInAccessor(ArrayBufferPrototype, 'detached', {
+    configurable: true,
+    get: function detached() {
+      return isDetached(this);
+    }
+  });
+}