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-pure/modules/es.reflect.delete-property.js

@@ -0,0 +1,16 @@
+'use strict';
+var $ = require('../internals/export');
+var anObject = require('../internals/an-object');
+var getOwnPropertyDescriptor = require('../internals/object-get-own-property-descriptor').f;
+var toPropertyKey = require('../internals/to-property-key');
+
+// `Reflect.deleteProperty` method
+// https://tc39.es/ecma262/#sec-reflect.deleteproperty
+$({ target: 'Reflect', stat: true }, {
+  deleteProperty: function deleteProperty(target, propertyKey) {
+    anObject(target);
+    var key = toPropertyKey(propertyKey);
+    var descriptor = getOwnPropertyDescriptor(target, key);
+    return descriptor && !descriptor.configurable ? false : delete target[key];
+  }
+});