Stand: SMTP-Test, Admin-Mail-Tab, Notifiable-Fix, Lazy-Quill

- Fix: Notifiable-Trait zum User-Model hinzugefuegt (behebt notify()-500er)
- Installer: SMTP-Verbindungstest mit EsmtpTransport + Ueberspringen-Link
- Admin: Neuer E-Mail-Tab mit SMTP-Konfiguration + Verbindungstest
- Admin: Lazy Quill-Initialisierung (nur sichtbare Locale wird geladen)
- Uebersetzungen: 17 neue Mail-Keys in allen 6 Sprachen

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

vendor/symfony/string/Resources/functions.php

@@ -0,0 +1,38 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\String;
+
+if (!\function_exists(u::class)) {
+    function u(?string $string = ''): UnicodeString
+    {
+        return new UnicodeString($string ?? '');
+    }
+}
+
+if (!\function_exists(b::class)) {
+    function b(?string $string = ''): ByteString
+    {
+        return new ByteString($string ?? '');
+    }
+}
+
+if (!\function_exists(s::class)) {
+    /**
+     * @return UnicodeString|ByteString
+     */
+    function s(?string $string = ''): AbstractString
+    {
+        $string ??= '';
+
+        return preg_match('//u', $string) ? new UnicodeString($string) : new ByteString($string);
+    }
+}