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/Portal/Portal.d.ts

@@ -0,0 +1,13 @@
+import * as React from "react";
+export declare type PortalProps = {
+    /**
+     * Portal's children.
+     */
+    children: React.ReactNode;
+};
+export declare const PortalContext: React.Context<HTMLElement | null>;
+export declare function Portal({ children }: PortalProps): React.ReactPortal | null;
+export declare namespace Portal {
+    var __className: string;
+    var __selector: string;
+}

node_modules/reakit/ts/Portal/index.d.ts

@@ -0,0 +1 @@
+export * from "./Portal";