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/2022/IsStringWellFormedUnicode.js

@@ -0,0 +1,23 @@
+'use strict';
+
+var CodePointAt = require('./CodePointAt');
+
+var $TypeError = require('es-errors/type');
+
+// https://262.ecma-international.org/13.0/#sec-isstringwellformedunicode
+
+module.exports = function IsStringWellFormedUnicode(string) {
+	if (typeof string !== 'string') {
+		throw new $TypeError('Assertion failed: `string` must be a String');
+	}
+	var strLen = string.length; // step 1
+	var k = 0; // step 2
+	while (k !== strLen) { // step 3
+		var cp = CodePointAt(string, k); // step 3.a
+		if (cp['[[IsUnpairedSurrogate]]']) {
+			return false; // step 3.b
+		}
+		k += cp['[[CodeUnitCount]]']; // step 3.c
+	}
+	return true; // step 4
+};