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/stylelint/lib/utils/configurationError.js

@@ -0,0 +1,16 @@
+'use strict';
+
+/** @typedef {import('stylelint').ConfigurationError} ConfigurationError */
+
+/**
+ * Create configurationError from text and set CLI exit code
+ * @param {string} text
+ * @returns {ConfigurationError}
+ */
+module.exports = function configurationError(text) {
+	const err = /** @type {ConfigurationError} */ (new Error(text));
+
+	err.code = 78;
+
+	return err;
+};