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/lib/Toolbar/ToolbarSeparator.js

@@ -0,0 +1,34 @@
+'use strict';
+
+Object.defineProperty(exports, '__esModule', { value: true });
+
+var _rollupPluginBabelHelpers = require('../_rollupPluginBabelHelpers-8f9a8751.js');
+var createComponent = require('reakit-system/createComponent');
+var createHook = require('reakit-system/createHook');
+require('reakit-utils/shallowEqual');
+require('../Role/Role.js');
+var Separator_Separator = require('../Separator/Separator.js');
+var __keys = require('../__keys-403ff944.js');
+
+var useToolbarSeparator = createHook.createHook({
+  name: "ToolbarSeparator",
+  compose: Separator_Separator.useSeparator,
+  keys: __keys.TOOLBAR_SEPARATOR_KEYS,
+  useOptions: function useOptions(_ref) {
+    var _ref$orientation = _ref.orientation,
+        orientation = _ref$orientation === void 0 ? "vertical" : _ref$orientation,
+        options = _rollupPluginBabelHelpers._objectWithoutPropertiesLoose(_ref, ["orientation"]);
+
+    return _rollupPluginBabelHelpers._objectSpread2({
+      orientation: orientation === "vertical" ? "horizontal" : "vertical"
+    }, options);
+  }
+});
+var ToolbarSeparator = createComponent.createComponent({
+  as: "hr",
+  memo: true,
+  useHook: useToolbarSeparator
+});
+
+exports.ToolbarSeparator = ToolbarSeparator;
+exports.useToolbarSeparator = useToolbarSeparator;