Enhance newsletter functionality with contact email support

- Added support for a contact email in newsletter generation, allowing users to specify a reply-to address.
- Updated the SMTP settings to include a reply-to field in the configuration.
- Modified the newsletter templates to display the contact email in plain text and HTML formats.
- Improved the dashboard UI to allow users to set the reply-to address when configuring SMTP settings.

app/templates/dashboard.html

@@ -253,9 +253,14 @@
                             <input type="password" name="password" value="{{ smtp.password }}">
                         </label>
                     </div>
-                    <label>Absender E-Mail
-                        <input type="email" name="from_email" value="{{ smtp.from_email }}">
-                    </label>
+                    <div class="form-row">
+                        <label>Absender E-Mail
+                            <input type="email" name="from_email" value="{{ smtp.from_email }}">
+                        </label>
+                        <label>Antwort-Adresse (Reply-To)
+                            <input type="email" name="reply_to" value="{{ smtp.reply_to }}" placeholder="wiki-team@firma.de">
+                        </label>
+                    </div>
                     <label class="checkbox">
                         <input type="checkbox" name="use_tls" value="true" {% if smtp.use_tls == "true" %}checked{% endif %}>
                         STARTTLS verwenden