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/TrimString.js

@@ -0,0 +1,27 @@
+'use strict';
+
+var trimStart = require('string.prototype.trimstart');
+var trimEnd = require('string.prototype.trimend');
+
+var $TypeError = require('es-errors/type');
+
+var RequireObjectCoercible = require('./RequireObjectCoercible');
+var ToString = require('./ToString');
+
+// https://262.ecma-international.org/10.0/#sec-trimstring
+
+module.exports = function TrimString(string, where) {
+	var str = RequireObjectCoercible(string);
+	var S = ToString(str);
+	var T;
+	if (where === 'start') {
+		T = trimStart(S);
+	} else if (where === 'end') {
+		T = trimEnd(S);
+	} else if (where === 'start+end') {
+		T = trimStart(trimEnd(S));
+	} else {
+		throw new $TypeError('Assertion failed: invalid `where` value; must be "start", "end", or "start+end"');
+	}
+	return T;
+};