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/modules/es.function.name.js

@@ -0,0 +1,26 @@
+'use strict';
+var DESCRIPTORS = require('../internals/descriptors');
+var FUNCTION_NAME_EXISTS = require('../internals/function-name').EXISTS;
+var uncurryThis = require('../internals/function-uncurry-this');
+var defineBuiltInAccessor = require('../internals/define-built-in-accessor');
+
+var FunctionPrototype = Function.prototype;
+var functionToString = uncurryThis(FunctionPrototype.toString);
+var nameRE = /function\b(?:\s|\/\*[\S\s]*?\*\/|\/\/[^\n\r]*[\n\r]+)*([^\s(/]*)/;
+var regExpExec = uncurryThis(nameRE.exec);
+var NAME = 'name';
+
+// Function instances `.name` property
+// https://tc39.es/ecma262/#sec-function-instances-name
+if (DESCRIPTORS && !FUNCTION_NAME_EXISTS) {
+  defineBuiltInAccessor(FunctionPrototype, NAME, {
+    configurable: true,
+    get: function () {
+      try {
+        return regExpExec(nameRE, functionToString(this))[1];
+      } catch (error) {
+        return '';
+      }
+    }
+  });
+}