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/services/smtp_sender.py

@@ -18,6 +18,7 @@ def get_smtp_settings(db: Session) -> dict[str, str]:
         "username": get_config(db, "smtp.username", ""),
         "password": get_config(db, "smtp.password", ""),
         "from_email": get_config(db, "smtp.from_email", ""),
+        "reply_to": get_config(db, "smtp.reply_to", ""),
         "use_tls": get_config(db, "smtp.use_tls", "true"),
         "recipients": get_config(db, "smtp.recipients", ""),
         # Zeitplan
@@ -91,6 +92,8 @@ def send_newsletter(
     msg["Subject"] = subject
     msg["From"] = settings["from_email"]
     msg["To"] = ", ".join(recipients)
+    if settings.get("reply_to"):
+        msg["Reply-To"] = settings["reply_to"]
 
     try:
         port = int(settings["port"])