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/Box/Box.ts

@@ -0,0 +1,42 @@
+import * as React from "react";
+import { createComponent } from "reakit-system/createComponent";
+import { createHook } from "reakit-system/createHook";
+import { shallowEqual } from "reakit-utils/shallowEqual";
+import { BOX_KEYS } from "./__keys";
+
+export type BoxOptions = {
+  /**
+   * Options passed to `reakit-system-*`
+   * @private
+   */
+  unstable_system?: any;
+};
+
+export type BoxHTMLProps = React.HTMLAttributes<any> &
+  React.RefAttributes<any> & {
+    /**
+     * Function returned by the hook to wrap the element to which html props
+     * will be passed.
+     */
+    wrapElement?: (element: React.ReactNode) => React.ReactNode;
+  };
+
+export type BoxProps = BoxOptions & BoxHTMLProps;
+
+export const useBox = createHook<BoxOptions, BoxHTMLProps>({
+  name: "Box",
+  keys: BOX_KEYS,
+  propsAreEqual(prev, next) {
+    const { unstable_system: prevSystem, ...prevProps } = prev;
+    const { unstable_system: nextSystem, ...nextProps } = next;
+    if (prevSystem !== nextSystem && !shallowEqual(prevSystem, nextSystem)) {
+      return false;
+    }
+    return shallowEqual(prevProps, nextProps);
+  },
+});
+
+export const Box = createComponent({
+  as: "div",
+  useHook: useBox,
+});