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/data-view-byte-offset/test/index.js

@@ -0,0 +1,31 @@
+'use strict';
+
+var test = require('tape');
+var forEach = require('for-each');
+var v = require('es-value-fixtures');
+var inspect = require('object-inspect');
+
+var dataViewByteOffset = require('../');
+
+test('dataViewByteOffset', function (t) {
+	forEach(
+		// @ts-expect-error TS sucks at [].concat
+		// eslint-disable-next-line no-extra-parens
+		/** @type {[...typeof v.primitives, ...typeof v.objects]} */ ([].concat(v.primitives, v.objects)),
+		function (nonDV) {
+			t['throws'](function () { dataViewByteOffset(nonDV); }, TypeError, inspect(nonDV) + ' is not a DataView');
+		}
+	);
+
+	t.test('DataView', { skip: typeof DataView !== 'function' }, function (st) {
+		var ab = new ArrayBuffer(42);
+		var dv = new DataView(ab, 2);
+
+		st.equal(dataViewByteOffset(dv), 2, inspect(dv) + ' has the same byteOffset originally passed to the DataView');
+		st.equal(dataViewByteOffset(dv), dv.byteOffset, inspect(dv) + ' has the same byteOffset as the buffer’s byteOffset');
+
+		st.end();
+	});
+
+	t.end();
+});