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/lodash/_baseSetToString.js

@@ -0,0 +1,22 @@
+var constant = require('./constant'),
+    defineProperty = require('./_defineProperty'),
+    identity = require('./identity');
+
+/**
+ * The base implementation of `setToString` without support for hot loop shorting.
+ *
+ * @private
+ * @param {Function} func The function to modify.
+ * @param {Function} string The `toString` result.
+ * @returns {Function} Returns `func`.
+ */
+var baseSetToString = !defineProperty ? identity : function(func, string) {
+  return defineProperty(func, 'toString', {
+    'configurable': true,
+    'enumerable': false,
+    'value': constant(string),
+    'writable': true
+  });
+};
+
+module.exports = baseSetToString;