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/argparse/lib/argparse.js

@@ -0,0 +1,14 @@
+'use strict';
+
+module.exports.ArgumentParser = require('./argument_parser.js');
+module.exports.Namespace = require('./namespace');
+module.exports.Action = require('./action');
+module.exports.HelpFormatter = require('./help/formatter.js');
+module.exports.Const = require('./const.js');
+
+module.exports.ArgumentDefaultsHelpFormatter =
+  require('./help/added_formatters.js').ArgumentDefaultsHelpFormatter;
+module.exports.RawDescriptionHelpFormatter =
+  require('./help/added_formatters.js').RawDescriptionHelpFormatter;
+module.exports.RawTextHelpFormatter =
+  require('./help/added_formatters.js').RawTextHelpFormatter;