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-scss/dist/utils/configurationError.js

@@ -0,0 +1,17 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+exports["default"] = _default;
+/**
+ * Create configurationError from text and set CLI exit code
+ *
+ * @param {string} text
+ * @return {Error} - The error, with text and exit code
+ */
+function _default(text) {
+  var err = new Error(text);
+  err.code = 78;
+  return err;
+}