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.map.group-by.js

@@ -0,0 +1,39 @@
+'use strict';
+var $ = require('../internals/export');
+var uncurryThis = require('../internals/function-uncurry-this');
+var aCallable = require('../internals/a-callable');
+var requireObjectCoercible = require('../internals/require-object-coercible');
+var iterate = require('../internals/iterate');
+var MapHelpers = require('../internals/map-helpers');
+var IS_PURE = require('../internals/is-pure');
+var fails = require('../internals/fails');
+
+var Map = MapHelpers.Map;
+var has = MapHelpers.has;
+var get = MapHelpers.get;
+var set = MapHelpers.set;
+var push = uncurryThis([].push);
+
+// https://bugs.webkit.org/show_bug.cgi?id=271524
+var DOES_NOT_WORK_WITH_PRIMITIVES = IS_PURE || fails(function () {
+  return Map.groupBy('ab', function (it) {
+    return it;
+  }).get('a').length !== 1;
+});
+
+// `Map.groupBy` method
+// https://tc39.es/ecma262/#sec-map.groupby
+$({ target: 'Map', stat: true, forced: IS_PURE || DOES_NOT_WORK_WITH_PRIMITIVES }, {
+  groupBy: function groupBy(items, callbackfn) {
+    requireObjectCoercible(items);
+    aCallable(callbackfn);
+    var map = new Map();
+    var k = 0;
+    iterate(items, function (value) {
+      var key = callbackfn(value, k++);
+      if (!has(map, key)) set(map, key, [value]);
+      else push(get(map, key), value);
+    });
+    return map;
+  }
+});