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/Checkbox/CheckboxState.js

@@ -0,0 +1,30 @@
+'use strict';
+
+Object.defineProperty(exports, '__esModule', { value: true });
+
+var React = require('react');
+var useSealedState = require('reakit-utils/useSealedState');
+
+/**
+ * As simple as `React.useState(false)`
+ */
+function useCheckboxState(initialState) {
+  if (initialState === void 0) {
+    initialState = {};
+  }
+
+  var _useSealedState = useSealedState.useSealedState(initialState),
+      _useSealedState$state = _useSealedState.state,
+      initialValue = _useSealedState$state === void 0 ? false : _useSealedState$state;
+
+  var _React$useState = React.useState(initialValue),
+      state = _React$useState[0],
+      setState = _React$useState[1];
+
+  return {
+    state: state,
+    setState: setState
+  };
+}
+
+exports.useCheckboxState = useCheckboxState;