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-syntax-json-strings/README.md

@@ -0,0 +1,19 @@
+# @babel/plugin-syntax-json-strings
+
+> Allow parsing of the U+2028 LINE SEPARATOR and U+2029 PARAGRAPH SEPARATOR in JS strings
+
+See our website [@babel/plugin-syntax-json-strings](https://babeljs.io/docs/en/next/babel-plugin-syntax-json-strings.html) for more information.
+
+## Install
+
+Using npm:
+
+```sh
+npm install --save-dev @babel/plugin-syntax-json-strings
+```
+
+or using yarn:
+
+```sh
+yarn add @babel/plugin-syntax-json-strings --dev
+```