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/configurator.js

@@ -0,0 +1,28 @@
+'use strict';
+var hasOwn = require('./internals/has-own-property');
+var isArray = require('./internals/is-array');
+var isForced = require('./internals/is-forced');
+var shared = require('./internals/shared-store');
+
+var data = isForced.data;
+var normalize = isForced.normalize;
+var USE_FUNCTION_CONSTRUCTOR = 'USE_FUNCTION_CONSTRUCTOR';
+var ASYNC_ITERATOR_PROTOTYPE = 'AsyncIteratorPrototype';
+
+var setAggressivenessLevel = function (object, constant) {
+  if (isArray(object)) for (var i = 0; i < object.length; i++) data[normalize(object[i])] = constant;
+};
+
+module.exports = function (options) {
+  if (options && typeof options == 'object') {
+    setAggressivenessLevel(options.useNative, isForced.NATIVE);
+    setAggressivenessLevel(options.usePolyfill, isForced.POLYFILL);
+    setAggressivenessLevel(options.useFeatureDetection, null);
+    if (hasOwn(options, USE_FUNCTION_CONSTRUCTOR)) {
+      shared[USE_FUNCTION_CONSTRUCTOR] = !!options[USE_FUNCTION_CONSTRUCTOR];
+    }
+    if (hasOwn(options, ASYNC_ITERATOR_PROTOTYPE)) {
+      shared[ASYNC_ITERATOR_PROTOTYPE] = options[ASYNC_ITERATOR_PROTOTYPE];
+    }
+  }
+};