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/MenuArrow.d.ts

@@ -0,0 +1,20 @@
+/// <reference types="react" />
+import { PopoverArrowOptions, PopoverArrowHTMLProps } from "../Popover/PopoverArrow";
+export declare type MenuArrowOptions = PopoverArrowOptions;
+export declare type MenuArrowHTMLProps = PopoverArrowHTMLProps;
+export declare type MenuArrowProps = MenuArrowOptions & MenuArrowHTMLProps;
+export declare const useMenuArrow: {
+    (options?: PopoverArrowOptions | undefined, htmlProps?: import("..").RoleHTMLProps | undefined, unstable_ignoreUseOptions?: boolean | undefined): import("..").RoleHTMLProps;
+    unstable_propsAreEqual: (prev: import("..").RoleOptions & Pick<Partial<import("..").PopoverStateReturn>, "unstable_arrowRef" | "unstable_arrowStyles"> & Pick<import("..").PopoverStateReturn, "placement"> & {
+        size?: string | number | undefined;
+    } & import("react").HTMLAttributes<any> & import("react").RefAttributes<any> & {
+        wrapElement?: ((element: import("react").ReactNode) => import("react").ReactNode) | undefined;
+    }, next: import("..").RoleOptions & Pick<Partial<import("..").PopoverStateReturn>, "unstable_arrowRef" | "unstable_arrowStyles"> & Pick<import("..").PopoverStateReturn, "placement"> & {
+        size?: string | number | undefined;
+    } & import("react").HTMLAttributes<any> & import("react").RefAttributes<any> & {
+        wrapElement?: ((element: import("react").ReactNode) => import("react").ReactNode) | undefined;
+    }) => boolean;
+    __keys: readonly any[];
+    __useOptions: (options: PopoverArrowOptions, htmlProps: import("..").RoleHTMLProps) => PopoverArrowOptions;
+};
+export declare const MenuArrow: import("reakit-system/ts/createComponent").Component<"div", PopoverArrowOptions>;