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/ts/Id/IdProvider.d.ts

@@ -0,0 +1,8 @@
+import * as React from "react";
+import { generateRandomString } from "./__utils";
+export declare type unstable_IdProviderProps = {
+    children: React.ReactNode;
+    prefix?: string;
+};
+export declare const unstable_IdContext: React.Context<typeof generateRandomString>;
+export declare function unstable_IdProvider({ children, prefix, }: unstable_IdProviderProps): JSX.Element;