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/shell-quote/test/comment.js

@@ -0,0 +1,16 @@
+'use strict';
+
+var test = require('tape');
+var parse = require('../').parse;
+
+test('comment', function (t) {
+	t.same(parse('beep#boop'), ['beep', { comment: 'boop' }]);
+	t.same(parse('beep #boop'), ['beep', { comment: 'boop' }]);
+	t.same(parse('beep # boop'), ['beep', { comment: ' boop' }]);
+	t.same(parse('beep # > boop'), ['beep', { comment: ' > boop' }]);
+	t.same(parse('beep # "> boop"'), ['beep', { comment: ' "> boop"' }]);
+	t.same(parse('beep "#"'), ['beep', '#']);
+	t.same(parse('beep #"#"#'), ['beep', { comment: '"#"#' }]);
+	t.same(parse('beep > boop # > foo'), ['beep', { op: '>' }, 'boop', { comment: ' > foo' }]);
+	t.end();
+});