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/css-tree/cjs/syntax/node/MediaFeatureRange.cjs

@@ -0,0 +1,11 @@
+'use strict';
+
+const featureRange = require('./common/feature-range.cjs');
+
+const name = 'MediaFeatureRange';
+const parse = featureRange.createParse(name);
+
+exports.generate = featureRange.generate;
+exports.structure = featureRange.structure;
+exports.name = name;
+exports.parse = parse;