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/babel-runtime/helpers/temporalRef.js

@@ -0,0 +1,11 @@
+"use strict";
+
+exports.__esModule = true;
+
+exports.default = function (val, name, undef) {
+  if (val === undef) {
+    throw new ReferenceError(name + " is not defined - temporal dead zone");
+  } else {
+    return val;
+  }
+};