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/esnext.data-view.set-uint8-clamped.js

@@ -0,0 +1,21 @@
+'use strict';
+var $ = require('../internals/export');
+var uncurryThis = require('../internals/function-uncurry-this');
+var aDataView = require('../internals/a-data-view');
+var toIndex = require('../internals/to-index');
+var toUint8Clamped = require('../internals/to-uint8-clamped');
+
+// eslint-disable-next-line es/no-typed-arrays -- safe
+var setUint8 = uncurryThis(DataView.prototype.setUint8);
+
+// `DataView.prototype.setUint8Clamped` method
+// https://github.com/tc39/proposal-dataview-get-set-uint8clamped
+$({ target: 'DataView', proto: true, forced: true }, {
+  setUint8Clamped: function setUint8Clamped(byteOffset, value) {
+    setUint8(
+      aDataView(this),
+      toIndex(byteOffset),
+      toUint8Clamped(value)
+    );
+  }
+});