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/UnableToMountFilesystem.php

@@ -0,0 +1,32 @@
+<?php
+
+declare(strict_types=1);
+
+namespace League\Flysystem;
+
+use LogicException;
+
+class UnableToMountFilesystem extends LogicException implements FilesystemException
+{
+    /**
+     * @param mixed $key
+     */
+    public static function becauseTheKeyIsNotValid($key): UnableToMountFilesystem
+    {
+        return new UnableToMountFilesystem(
+            'Unable to mount filesystem, key was invalid. String expected, received: ' . gettype($key)
+        );
+    }
+
+    /**
+     * @param mixed $filesystem
+     */
+    public static function becauseTheFilesystemWasNotValid($filesystem): UnableToMountFilesystem
+    {
+        $received = is_object($filesystem) ? get_class($filesystem) : gettype($filesystem);
+
+        return new UnableToMountFilesystem(
+            'Unable to mount filesystem, filesystem was invalid. Instance of ' . FilesystemOperator::class . ' expected, received: ' . $received
+        );
+    }
+}