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/2025/StringPaddingBuiltinsImpl.js

@@ -0,0 +1,27 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var StringPad = require('./StringPad');
+var ToLength = require('./ToLength');
+var ToString = require('./ToString');
+
+// https://262.ecma-international.org/15.0/#sec-stringpaddingbuiltinsimpl
+
+module.exports = function StringPaddingBuiltinsImpl(O, maxLength, fillString, placement) {
+	if (placement !== 'start' && placement !== 'end' && placement !== 'START' && placement !== 'END') {
+		throw new $TypeError('Assertion failed: `placement` must be ~START~ or ~END~');
+	}
+
+	var S = ToString(O); // step 1
+
+	var intMaxLength = ToLength(maxLength); // step 2
+
+	var stringLength = S.length; // step 3
+
+	if (intMaxLength <= stringLength) { return S; } // step 4
+
+	var filler = typeof fillString === 'undefined' ? ' ' : ToString(fillString); // steps 5-6
+
+	return StringPad(S, intMaxLength, filler, placement); // step 7
+};