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/reakit/src/Portal/README.md

@@ -0,0 +1,33 @@
+---
+path: /docs/portal/
+redirect_from:
+  - /components/portal/
+---
+
+# Portal
+
+`Portal` is an abstract wrapper component that uses [React Portals](https://reactjs.org/docs/portals.html) underneath. It can be used to put anything in a portal and supports nested portals.
+
+<carbon-ad></carbon-ad>
+
+## Installation
+
+```sh
+npm install reakit
+```
+
+Learn more in [Get started](/docs/get-started/).
+
+## Usage
+
+```jsx
+import { Portal } from "reakit/Portal";
+
+function Example() {
+  return (
+    <div style={{ background: "red", color: "white" }}>
+      I am here, <Portal>but I am detached at the bottom of the page.</Portal>
+    </div>
+  );
+}
+```