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/lighthouse/report/renderer/swap-locale-feature.js

@@ -0,0 +1,76 @@
+/**
+ * @license Copyright 2021 The Lighthouse Authors. All Rights Reserved.
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
+ */
+
+/**
+ * @fileoverview Creates a <select> element, filled with all supported locales
+ */
+
+/** @typedef {import('./dom.js').DOM} DOM */
+/** @typedef {import('./report-ui-features').ReportUIFeatures} ReportUIFeatures */
+
+export class SwapLocaleFeature {
+  /**
+   * @param {ReportUIFeatures} reportUIFeatures
+   * @param {DOM} dom
+   * @param {{onLocaleSelected: (localeModuleName: LH.Locale) => Promise<void>}} callbacks
+   *        Specifiy the URL where the i18n module script can be found, and the URLS for the locale JSON files.
+   */
+  constructor(reportUIFeatures, dom, callbacks) {
+    this._reportUIFeatures = reportUIFeatures;
+    this._dom = dom;
+    this._localeSelectedCallback = callbacks.onLocaleSelected;
+  }
+
+  /**
+   * @param {Array<LH.Locale>} locales
+   */
+  enable(locales) {
+    if (!this._reportUIFeatures.json.i18n.icuMessagePaths) {
+      throw new Error('missing icuMessagePaths');
+    }
+
+    this._dom.find('.lh-tools-locale', this._dom.rootEl).classList.remove('lh-hidden');
+
+    const currentLocale = this._reportUIFeatures.json.configSettings.locale;
+
+    const containerEl = this._dom.find('.lh-tools-locale__selector-wrapper', this._dom.rootEl);
+    containerEl.removeAttribute('aria-hidden');
+    const selectEl = this._dom.createChildOf(containerEl, 'select', 'lh-locale-selector');
+    selectEl.name = 'lh-locale-list';
+    selectEl.setAttribute('role', 'menuitem');
+
+    const toggleEl = this._dom.find('.lh-tool-locale__button', this._dom.rootEl);
+    toggleEl.addEventListener('click', () => {
+      toggleEl.classList.toggle('lh-active');
+    });
+
+    for (const locale of locales) {
+      const optionEl = this._dom.createChildOf(selectEl, 'option', '');
+      optionEl.value = locale;
+      if (locale === currentLocale) optionEl.selected = true;
+
+      if (window.Intl && Intl.DisplayNames) {
+        const currentLocaleDisplay = new Intl.DisplayNames([currentLocale], {type: 'language'});
+        const optionLocaleDisplay = new Intl.DisplayNames([locale], {type: 'language'});
+
+        const optionLocaleName = optionLocaleDisplay.of(locale);
+        const currentLocaleName = currentLocaleDisplay.of(locale) || locale;
+        if (optionLocaleName && optionLocaleName !== currentLocaleName) {
+          optionEl.textContent = `${optionLocaleName} – ${currentLocaleName}`;
+        } else {
+          optionEl.textContent = currentLocaleName;
+        }
+      } else {
+        optionEl.textContent = locale;
+      }
+    }
+
+    selectEl.addEventListener('change', () => {
+      const locale = /** @type {LH.Locale} */ (selectEl.value);
+      this._localeSelectedCallback(locale);
+    });
+  }
+}