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-pure/internals/function-name.js

@@ -0,0 +1,18 @@
+'use strict';
+var DESCRIPTORS = require('../internals/descriptors');
+var hasOwn = require('../internals/has-own-property');
+
+var FunctionPrototype = Function.prototype;
+// eslint-disable-next-line es/no-object-getownpropertydescriptor -- safe
+var getDescriptor = DESCRIPTORS && Object.getOwnPropertyDescriptor;
+
+var EXISTS = hasOwn(FunctionPrototype, 'name');
+// additional protection from minified / mangled / dropped function names
+var PROPER = EXISTS && function something() { /* empty */ }.name === 'something';
+var CONFIGURABLE = EXISTS && (!DESCRIPTORS || (DESCRIPTORS && getDescriptor(FunctionPrototype, 'name').configurable));
+
+module.exports = {
+  EXISTS: EXISTS,
+  PROPER: PROPER,
+  CONFIGURABLE: CONFIGURABLE
+};