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/esnext.reflect.get-metadata.js

@@ -0,0 +1,26 @@
+'use strict';
+// TODO: Remove from `core-js@4`
+var $ = require('../internals/export');
+var ReflectMetadataModule = require('../internals/reflect-metadata');
+var anObject = require('../internals/an-object');
+var getPrototypeOf = require('../internals/object-get-prototype-of');
+
+var ordinaryHasOwnMetadata = ReflectMetadataModule.has;
+var ordinaryGetOwnMetadata = ReflectMetadataModule.get;
+var toMetadataKey = ReflectMetadataModule.toKey;
+
+var ordinaryGetMetadata = function (MetadataKey, O, P) {
+  var hasOwn = ordinaryHasOwnMetadata(MetadataKey, O, P);
+  if (hasOwn) return ordinaryGetOwnMetadata(MetadataKey, O, P);
+  var parent = getPrototypeOf(O);
+  return parent !== null ? ordinaryGetMetadata(MetadataKey, parent, P) : undefined;
+};
+
+// `Reflect.getMetadata` method
+// https://github.com/rbuckton/reflect-metadata
+$({ target: 'Reflect', stat: true }, {
+  getMetadata: function getMetadata(metadataKey, target /* , targetKey */) {
+    var targetKey = arguments.length < 3 ? undefined : toMetadataKey(arguments[2]);
+    return ordinaryGetMetadata(metadataKey, anObject(target), targetKey);
+  }
+});