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/league/flysystem/src/UnableToListContents.php

@@ -0,0 +1,24 @@
+<?php
+
+declare(strict_types=1);
+
+namespace League\Flysystem;
+
+use RuntimeException;
+use Throwable;
+
+final class UnableToListContents extends RuntimeException implements FilesystemOperationFailed
+{
+    public static function atLocation(string $location, bool $deep, Throwable $previous): UnableToListContents
+    {
+        $message = "Unable to list contents for '$location', " . ($deep ? 'deep' : 'shallow') . " listing\n\n"
+            . 'Reason: ' . $previous->getMessage();
+
+        return new UnableToListContents($message, 0, $previous);
+    }
+
+    public function operation(): string
+    {
+        return self::OPERATION_LIST_CONTENTS;
+    }
+}