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/es.array.reverse.js

@@ -0,0 +1,19 @@
+'use strict';
+var $ = require('../internals/export');
+var uncurryThis = require('../internals/function-uncurry-this');
+var isArray = require('../internals/is-array');
+
+var nativeReverse = uncurryThis([].reverse);
+var test = [1, 2];
+
+// `Array.prototype.reverse` method
+// https://tc39.es/ecma262/#sec-array.prototype.reverse
+// fix for Safari 12.0 bug
+// https://bugs.webkit.org/show_bug.cgi?id=188794
+$({ target: 'Array', proto: true, forced: String(test) === String(test.reverse()) }, {
+  reverse: function reverse() {
+    // eslint-disable-next-line no-self-assign -- dirty hack
+    if (isArray(this)) this.length = this.length;
+    return nativeReverse(this);
+  }
+});