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/@wordpress/components/build-module/tree-grid/roving-tab-index-item.js

@@ -0,0 +1,48 @@
+import { createElement } from "react";
+/**
+ * WordPress dependencies
+ */
+import { useRef, forwardRef } from '@wordpress/element';
+
+/**
+ * Internal dependencies
+ */
+import { useRovingTabIndexContext } from './roving-tab-index-context';
+export const RovingTabIndexItem = forwardRef(function UnforwardedRovingTabIndexItem({
+  children,
+  as: Component,
+  ...props
+}, forwardedRef) {
+  const localRef = useRef();
+  const ref = forwardedRef || localRef;
+  // @ts-expect-error - We actually want to throw an error if this is undefined.
+  const {
+    lastFocusedElement,
+    setLastFocusedElement
+  } = useRovingTabIndexContext();
+  let tabIndex;
+  if (lastFocusedElement) {
+    tabIndex = lastFocusedElement === (
+    // TODO: The original implementation simply used `ref.current` here, assuming
+    // that a forwarded ref would always be an object, which is not necessarily true.
+    // This workaround maintains the original runtime behavior in a type-safe way,
+    // but should be revisited.
+    'current' in ref ? ref.current : undefined) ? 0 : -1;
+  }
+  const onFocus = event => setLastFocusedElement?.(event.target);
+  const allProps = {
+    ref,
+    tabIndex,
+    onFocus,
+    ...props
+  };
+  if (typeof children === 'function') {
+    return children(allProps);
+  }
+  if (!Component) return null;
+  return createElement(Component, {
+    ...allProps
+  }, children);
+});
+export default RovingTabIndexItem;
+//# sourceMappingURL=roving-tab-index-item.js.map