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/is-extglob/index.js

@@ -0,0 +1,20 @@
+/*!
+ * is-extglob <https://github.com/jonschlinkert/is-extglob>
+ *
+ * Copyright (c) 2014-2016, Jon Schlinkert.
+ * Licensed under the MIT License.
+ */
+
+module.exports = function isExtglob(str) {
+  if (typeof str !== 'string' || str === '') {
+    return false;
+  }
+
+  var match;
+  while ((match = /(\\).|([@?!+*]\(.*\))/g.exec(str))) {
+    if (match[2]) return true;
+    str = str.slice(match.index + match[0].length);
+  }
+
+  return false;
+};