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/babel-plugin-polyfill-corejs2/README.md

@@ -0,0 +1,28 @@
+# babel-plugin-polyfill-corejs2
+
+## Install
+
+Using npm:
+
+```sh
+npm install --save-dev babel-plugin-polyfill-corejs2
+```
+
+or using yarn:
+
+```sh
+yarn add babel-plugin-polyfill-corejs2 --dev
+```
+
+## Usage
+
+Add this plugin to your Babel configuration:
+
+```json
+{
+  "plugins": [["polyfill-corejs2", { "method": "usage-global" }]]
+}
+```
+
+This package supports the `usage-pure`, `usage-global`, and `entry-global` methods.
+When `entry-global` is used, it replaces imports to `core-js`.