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/array-buffer-byte-length/index.js

@@ -0,0 +1,14 @@
+'use strict';
+
+var callBound = require('call-bound');
+var $byteLength = callBound('ArrayBuffer.prototype.byteLength', true);
+
+var isArrayBuffer = require('is-array-buffer');
+
+/** @type {import('.')} */
+module.exports = function byteLength(ab) {
+	if (!isArrayBuffer(ab)) {
+		return NaN;
+	}
+	return $byteLength ? $byteLength(ab) : ab.byteLength;
+}; // in node < 0.11, byteLength is an own nonconfigurable property