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/placeholder/index.js

@@ -0,0 +1,92 @@
+import { createElement } from "react";
+/**
+ * External dependencies
+ */
+import classnames from 'classnames';
+
+/**
+ * WordPress dependencies
+ */
+import { useResizeObserver } from '@wordpress/compose';
+import { SVG, Path } from '@wordpress/primitives';
+import { useEffect } from '@wordpress/element';
+import { speak } from '@wordpress/a11y';
+
+/**
+ * Internal dependencies
+ */
+import Icon from '../icon';
+const PlaceholderIllustration = createElement(SVG, {
+  className: "components-placeholder__illustration",
+  fill: "none",
+  xmlns: "http://www.w3.org/2000/svg",
+  viewBox: "0 0 60 60",
+  preserveAspectRatio: "none"
+}, createElement(Path, {
+  vectorEffect: "non-scaling-stroke",
+  d: "M60 60 0 0"
+}));
+
+/**
+ * Renders a placeholder. Normally used by blocks to render their empty state.
+ *
+ * ```jsx
+ * import { Placeholder } from '@wordpress/components';
+ * import { more } from '@wordpress/icons';
+ *
+ * const MyPlaceholder = () => <Placeholder icon={ more } label="Placeholder" />;
+ * ```
+ */
+export function Placeholder(props) {
+  const {
+    icon,
+    children,
+    label,
+    instructions,
+    className,
+    notices,
+    preview,
+    isColumnLayout,
+    withIllustration,
+    ...additionalProps
+  } = props;
+  const [resizeListener, {
+    width
+  }] = useResizeObserver();
+
+  // Since `useResizeObserver` will report a width of `null` until after the
+  // first render, avoid applying any modifier classes until width is known.
+  let modifierClassNames;
+  if (typeof width === 'number') {
+    modifierClassNames = {
+      'is-large': width >= 480,
+      'is-medium': width >= 160 && width < 480,
+      'is-small': width < 160
+    };
+  }
+  const classes = classnames('components-placeholder', className, modifierClassNames, withIllustration ? 'has-illustration' : null);
+  const fieldsetClasses = classnames('components-placeholder__fieldset', {
+    'is-column-layout': isColumnLayout
+  });
+  useEffect(() => {
+    if (instructions) {
+      speak(instructions);
+    }
+  }, [instructions]);
+  return createElement("div", {
+    ...additionalProps,
+    className: classes
+  }, withIllustration ? PlaceholderIllustration : null, resizeListener, notices, preview && createElement("div", {
+    className: "components-placeholder__preview"
+  }, preview), createElement("div", {
+    className: "components-placeholder__label"
+  }, createElement(Icon, {
+    icon: icon
+  }), label), !!instructions && createElement("div", {
+    className: "components-placeholder__instructions"
+  }, instructions), createElement("div", {
+    className: fieldsetClasses
+  }, children));
+}
+export default Placeholder;
+//# sourceMappingURL=index.js.map

node_modules/@wordpress/components/build-module/placeholder/types.js

@@ -0,0 +1,2 @@
+export {};
+//# sourceMappingURL=types.js.map

node_modules/@wordpress/components/build-module/placeholder/types.js.map

@@ -0,0 +1 @@
+{"version":3,"names":[],"sources":["@wordpress/components/src/placeholder/types.ts"],"sourcesContent":["/**\n * External dependencies\n */\nimport type { ReactNode } from 'react';\n\n/**\n * Internal dependencies\n */\nimport type { IconType } from '../icon';\n\nexport type PlaceholderProps = {\n\t/**\n\t * The children elements.\n\t */\n\tchildren?: ReactNode;\n\t/**\n\t * Class to set on the container div.\n\t */\n\tclassName?: string;\n\t/**\n\t * If provided, renders an icon next to the label.\n\t */\n\ticon?: IconType;\n\t/**\n\t * Instructions of the placeholder.\n\t */\n\tinstructions?: string;\n\t/**\n\t * Changes placeholder children layout from flex-row to flex-column.\n\t */\n\tisColumnLayout?: boolean;\n\t/**\n\t * Title of the placeholder.\n\t */\n\tlabel?: string;\n\t/**\n\t * A rendered notices list\n\t */\n\tnotices?: ReactNode;\n\t/**\n\t * Preview to be rendered in the placeholder.\n\t */\n\tpreview?: ReactNode;\n\t/**\n\t * Outputs a placeholder illustration.\n\t */\n\twithIllustration?: boolean;\n};\n"],"mappings":""}