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/CalculateChecksumFromStream.php

@@ -0,0 +1,30 @@
+<?php
+declare(strict_types=1);
+
+namespace League\Flysystem;
+
+use function hash_final;
+use function hash_init;
+use function hash_update_stream;
+
+trait CalculateChecksumFromStream
+{
+    private function calculateChecksumFromStream(string $path, Config $config): string
+    {
+        try {
+            $stream = $this->readStream($path);
+            $algo = (string) $config->get('checksum_algo', 'md5');
+            $context = hash_init($algo);
+            hash_update_stream($context, $stream);
+
+            return hash_final($context);
+        } catch (FilesystemException $exception) {
+            throw new UnableToProvideChecksum($exception->getMessage(), $path, $exception);
+        }
+    }
+
+    /**
+     * @return resource
+     */
+    abstract public function readStream(string $path);
+}