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/jest-validate/build/condition.js

@@ -0,0 +1,44 @@
+'use strict';
+
+Object.defineProperty(exports, '__esModule', {
+  value: true
+});
+exports.getValues = getValues;
+exports.multipleValidOptions = multipleValidOptions;
+exports.validationCondition = validationCondition;
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+const toString = Object.prototype.toString;
+const MULTIPLE_VALID_OPTIONS_SYMBOL = Symbol('JEST_MULTIPLE_VALID_OPTIONS');
+function validationConditionSingle(option, validOption) {
+  return (
+    option === null ||
+    option === undefined ||
+    (typeof option === 'function' && typeof validOption === 'function') ||
+    toString.call(option) === toString.call(validOption)
+  );
+}
+function getValues(validOption) {
+  if (
+    Array.isArray(validOption) &&
+    // @ts-expect-error: no index signature
+    validOption[MULTIPLE_VALID_OPTIONS_SYMBOL]
+  ) {
+    return validOption;
+  }
+  return [validOption];
+}
+function validationCondition(option, validOption) {
+  return getValues(validOption).some(e => validationConditionSingle(option, e));
+}
+function multipleValidOptions(...args) {
+  const options = [...args];
+  // @ts-expect-error: no index signature
+  options[MULTIPLE_VALID_OPTIONS_SYMBOL] = true;
+  return options;
+}