Fix start url for app deep links with domain

fragdenstaat_de/theme/views.py

@@ -2,6 +2,7 @@
 import urllib.parse
 from io import BytesIO
 
+from django.conf import settings
 from django.contrib import messages
 from django.contrib.auth.decorators import login_required
 from django.http import JsonResponse
@@ -101,7 +102,7 @@ def scannerapp_postupload(request, message_type, message_pk):
     in Scanner app
     """
     message_type = "draft" if message_type == "draft" else "message"
-    app_url = f"/app/scanner/deep/{message_type}/{message_pk}/"
+    app_url = f"{settings.SITE_URL}/app/scanner/deep/{message_type}/{message_pk}/"
 
     if request.user.can_autologin():
         login_url = request.user.get_autologin_url()