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/minimist/test/parse_modified.js

@@ -0,0 +1,11 @@
+'use strict';
+
+var parse = require('../');
+var test = require('tape');
+
+test('parse with modifier functions', function (t) {
+	t.plan(1);
+
+	var argv = parse(['-b', '123'], { boolean: 'b' });
+	t.deepEqual(argv, { b: true, _: [123] });
+});