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/Menu/__utils/MenuContext.d.ts

@@ -0,0 +1,15 @@
+import * as React from "react";
+import { MenuBarOptions } from "../MenuBar";
+import { MenuOptions } from "../Menu";
+declare type Ref = React.RefObject<HTMLElement>;
+export declare type MenuContextType = Pick<MenuBarOptions, "orientation" | "next" | "previous"> & {
+    ref: Ref;
+    role: string;
+    parent?: MenuContextType | null;
+    children: Array<Ref>;
+    addChild: (ref: Ref) => void;
+    removeChild: (ref: Ref) => void;
+};
+export declare const MenuContext: React.Context<MenuContextType | null>;
+export declare function useMenuContext(menuRef: Ref, role: string, options: MenuBarOptions | MenuOptions): (element: React.ReactNode) => JSX.Element;
+export {};