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/es-abstract/2018/UTF16Decode.js

@@ -0,0 +1,21 @@
+'use strict';
+
+var GetIntrinsic = require('get-intrinsic');
+
+var $TypeError = require('es-errors/type');
+var $fromCharCode = GetIntrinsic('%String.fromCharCode%');
+
+// https://262.ecma-international.org/7.0/#sec-utf16decode
+
+var isLeadingSurrogate = require('../helpers/isLeadingSurrogate');
+var isTrailingSurrogate = require('../helpers/isTrailingSurrogate');
+
+// https://262.ecma-international.org/11.0/#sec-utf16decodesurrogatepair
+
+module.exports = function UTF16Decode(lead, trail) {
+	if (!isLeadingSurrogate(lead) || !isTrailingSurrogate(trail)) {
+		throw new $TypeError('Assertion failed: `lead` must be a leading surrogate char code, and `trail` must be a trailing surrogate char code');
+	}
+	// var cp = (lead - 0xD800) * 0x400 + (trail - 0xDC00) + 0x10000;
+	return $fromCharCode(lead) + $fromCharCode(trail);
+};