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.json.is-raw-json.js

@@ -0,0 +1,11 @@
+'use strict';
+var $ = require('../internals/export');
+var NATIVE_RAW_JSON = require('../internals/native-raw-json');
+var isRawJSON = require('../internals/is-raw-json');
+
+// `JSON.isRawJSON` method
+// https://tc39.es/proposal-json-parse-with-source/#sec-json.israwjson
+// https://github.com/tc39/proposal-json-parse-with-source
+$({ target: 'JSON', stat: true, forced: !NATIVE_RAW_JSON }, {
+  isRawJSON: isRawJSON
+});