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/core-js/internals/function-bind-native.js

@@ -0,0 +1,9 @@
+'use strict';
+var fails = require('../internals/fails');
+
+module.exports = !fails(function () {
+  // eslint-disable-next-line es/no-function-prototype-bind -- safe
+  var test = function () { /* empty */ }.bind();
+  // eslint-disable-next-line no-prototype-builtins -- safe
+  return typeof test != 'function' || test.hasOwnProperty('prototype');
+});