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/mime/Header/HeaderInterface.php

@@ -0,0 +1,61 @@
+<?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\Mime\Header;
+
+/**
+ * A MIME Header.
+ *
+ * @author Chris Corbyn
+ */
+interface HeaderInterface
+{
+    /**
+     * Sets the body.
+     *
+     * The type depends on the Header concrete class.
+     */
+    public function setBody(mixed $body): void;
+
+    /**
+     * Gets the body.
+     *
+     * The return type depends on the Header concrete class.
+     */
+    public function getBody(): mixed;
+
+    public function setCharset(string $charset): void;
+
+    public function getCharset(): ?string;
+
+    public function setLanguage(string $lang): void;
+
+    public function getLanguage(): ?string;
+
+    public function getName(): string;
+
+    public function setMaxLineLength(int $lineLength): void;
+
+    public function getMaxLineLength(): int;
+
+    /**
+     * Gets this Header rendered as a compliant string.
+     */
+    public function toString(): string;
+
+    /**
+     * Gets the header's body, prepared for folding into a final header value.
+     *
+     * This is not necessarily RFC 2822 compliant since folding white space is
+     * not added at this stage (see {@link toString()} for that).
+     */
+    public function getBodyAsString(): string;
+}