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/compose/build-module/hooks/use-constrained-tabbing/index.js

@@ -0,0 +1,88 @@
+/**
+ * WordPress dependencies
+ */
+import { focus } from '@wordpress/dom';
+
+/**
+ * Internal dependencies
+ */
+import useRefEffect from '../use-ref-effect';
+
+/**
+ * In Dialogs/modals, the tabbing must be constrained to the content of
+ * the wrapper element. This hook adds the behavior to the returned ref.
+ *
+ * @return {import('react').RefCallback<Element>} Element Ref.
+ *
+ * @example
+ * ```js
+ * import { useConstrainedTabbing } from '@wordpress/compose';
+ *
+ * const ConstrainedTabbingExample = () => {
+ *     const constrainedTabbingRef = useConstrainedTabbing()
+ *     return (
+ *         <div ref={ constrainedTabbingRef }>
+ *             <Button />
+ *             <Button />
+ *         </div>
+ *     );
+ * }
+ * ```
+ */
+function useConstrainedTabbing() {
+  return useRefEffect(( /** @type {HTMLElement} */node) => {
+    function onKeyDown( /** @type {KeyboardEvent} */event) {
+      const {
+        key,
+        shiftKey,
+        target
+      } = event;
+      if (key !== 'Tab') {
+        return;
+      }
+      const action = shiftKey ? 'findPrevious' : 'findNext';
+      const nextElement = focus.tabbable[action]( /** @type {HTMLElement} */target) || null;
+
+      // When the target element contains the element that is about to
+      // receive focus, for example when the target is a tabbable
+      // container, browsers may disagree on where to move focus next.
+      // In this case we can't rely on native browsers behavior. We need
+      // to manage focus instead.
+      // See https://github.com/WordPress/gutenberg/issues/46041.
+      if ( /** @type {HTMLElement} */target.contains(nextElement)) {
+        event.preventDefault();
+        nextElement?.focus();
+        return;
+      }
+
+      // If the element that is about to receive focus is inside the
+      // area, rely on native browsers behavior and let tabbing follow
+      // the native tab sequence.
+      if (node.contains(nextElement)) {
+        return;
+      }
+
+      // If the element that is about to receive focus is outside the
+      // area, move focus to a div and insert it at the start or end of
+      // the area, depending on the direction. Without preventing default
+      // behaviour, the browser will then move focus to the next element.
+      const domAction = shiftKey ? 'append' : 'prepend';
+      const {
+        ownerDocument
+      } = node;
+      const trap = ownerDocument.createElement('div');
+      trap.tabIndex = -1;
+      node[domAction](trap);
+
+      // Remove itself when the trap loses focus.
+      trap.addEventListener('blur', () => node.removeChild(trap));
+      trap.focus();
+    }
+    node.addEventListener('keydown', onKeyDown);
+    return () => {
+      node.removeEventListener('keydown', onKeyDown);
+    };
+  }, []);
+}
+export default useConstrainedTabbing;
+//# sourceMappingURL=index.js.map

node_modules/@wordpress/compose/build-module/hooks/use-constrained-tabbing/index.js.map

@@ -0,0 +1 @@
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node_modules/@wordpress/compose/build-module/hooks/use-constrained-tabbing/index.native.js

@@ -0,0 +1,13 @@
+/**
+ * WordPress dependencies
+ */
+import { useRef } from '@wordpress/element';
+function useConstrainedTabbing() {
+  const ref = useRef();
+
+  // Do nothing on mobile as tabbing is not a mobile behavior.
+
+  return ref;
+}
+export default useConstrainedTabbing;
+//# sourceMappingURL=index.native.js.map

node_modules/@wordpress/compose/build-module/hooks/use-constrained-tabbing/index.native.js.map

@@ -0,0 +1 @@
+{"version":3,"names":["useRef","useConstrainedTabbing","ref"],"sources":["@wordpress/compose/src/hooks/use-constrained-tabbing/index.native.js"],"sourcesContent":["/**\n * WordPress dependencies\n */\nimport { useRef } from '@wordpress/element';\n\nfunction useConstrainedTabbing() {\n\tconst ref = useRef();\n\n\t// Do nothing on mobile as tabbing is not a mobile behavior.\n\n\treturn ref;\n}\n\nexport default useConstrainedTabbing;\n"],"mappings":"AAAA;AACA;AACA;AACA,SAASA,MAAM,QAAQ,oBAAoB;AAE3C,SAASC,qBAAqBA,CAAA,EAAG;EAChC,MAAMC,GAAG,GAAGF,MAAM,CAAC,CAAC;;EAEpB;;EAEA,OAAOE,GAAG;AACX;AAEA,eAAeD,qBAAqB","ignoreList":[]}