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/core-js/modules/web.set-interval.js

@@ -0,0 +1,12 @@
+'use strict';
+var $ = require('../internals/export');
+var globalThis = require('../internals/global-this');
+var schedulersFix = require('../internals/schedulers-fix');
+
+var setInterval = schedulersFix(globalThis.setInterval, true);
+
+// Bun / IE9- setInterval additional parameters fix
+// https://html.spec.whatwg.org/multipage/timers-and-user-prompts.html#dom-setinterval
+$({ global: true, bind: true, forced: globalThis.setInterval !== setInterval }, {
+  setInterval: setInterval
+});