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/http-kernel/Exception/ServiceUnavailableHttpException.php

@@ -0,0 +1,30 @@
+<?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\HttpKernel\Exception;
+
+/**
+ * @author Ben Ramsey <ben@benramsey.com>
+ */
+class ServiceUnavailableHttpException extends HttpException
+{
+    /**
+     * @param int|string|null $retryAfter The number of seconds or HTTP-date after which the request may be retried
+     */
+    public function __construct(int|string|null $retryAfter = null, string $message = '', ?\Throwable $previous = null, int $code = 0, array $headers = [])
+    {
+        if ($retryAfter) {
+            $headers['Retry-After'] = $retryAfter;
+        }
+
+        parent::__construct(503, $message, $previous, $headers, $code);
+    }
+}