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.promise.catch.js

@@ -0,0 +1,26 @@
+'use strict';
+var $ = require('../internals/export');
+var IS_PURE = require('../internals/is-pure');
+var FORCED_PROMISE_CONSTRUCTOR = require('../internals/promise-constructor-detection').CONSTRUCTOR;
+var NativePromiseConstructor = require('../internals/promise-native-constructor');
+var getBuiltIn = require('../internals/get-built-in');
+var isCallable = require('../internals/is-callable');
+var defineBuiltIn = require('../internals/define-built-in');
+
+var NativePromisePrototype = NativePromiseConstructor && NativePromiseConstructor.prototype;
+
+// `Promise.prototype.catch` method
+// https://tc39.es/ecma262/#sec-promise.prototype.catch
+$({ target: 'Promise', proto: true, forced: FORCED_PROMISE_CONSTRUCTOR, real: true }, {
+  'catch': function (onRejected) {
+    return this.then(undefined, onRejected);
+  }
+});
+
+// makes sure that native promise-based APIs `Promise#catch` properly works with patched `Promise#then`
+if (!IS_PURE && isCallable(NativePromiseConstructor)) {
+  var method = getBuiltIn('Promise').prototype['catch'];
+  if (NativePromisePrototype['catch'] !== method) {
+    defineBuiltIn(NativePromisePrototype, 'catch', method, { unsafe: true });
+  }
+}