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/2023/IsWordChar.js

@@ -0,0 +1,42 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+var callBound = require('call-bound');
+var isInteger = require('math-intrinsics/isInteger');
+
+var $indexOf = callBound('String.prototype.indexOf');
+
+var IsArray = require('./IsArray');
+var WordCharacters = require('./WordCharacters');
+
+var every = require('../helpers/every');
+var isRegExpRecord = require('../helpers/records/regexp-record');
+
+var isChar = function isChar(c) {
+	return typeof c === 'string';
+};
+
+// https://262.ecma-international.org/14.0/#sec-runtime-semantics-iswordchar-abstract-operation
+
+module.exports = function IsWordChar(rer, Input, e) {
+	if (!isRegExpRecord(rer)) {
+		throw new $TypeError('Assertion failed: `rer` must be a RegExp Record');
+	}
+	if (!IsArray(Input) || !every(Input, isChar)) {
+		throw new $TypeError('Assertion failed: `Input` must be a List of characters');
+	}
+
+	if (!isInteger(e)) {
+		throw new $TypeError('Assertion failed: `e` must be an integer');
+	}
+
+	var InputLength = Input.length; // step 1
+
+	if (e === -1 || e === InputLength) {
+		return false; // step 2
+	}
+
+	var c = Input[e]; // step 3
+
+	return $indexOf(WordCharacters(rer), c) > -1; // steps 4-5
+};