feat(backend): improve comms around registration (#9932)

* use better email check

* add error code for missing email settings

* Add note when not registration is enabled

* fix wrong call

* fix tests - might be worth checking if the blank check for testing is a good idea

* capture issues and print to find out what the duck is going on

* exend log

* fix context check

src/frontend/src/components/forms/AuthenticationForm.tsx

@@ -3,6 +3,7 @@ import { apiUrl } from '@lib/functions/Api';
 import { t } from '@lingui/core/macro';
 import { Trans } from '@lingui/react/macro';
 import {
+  Alert,
   Anchor,
   Button,
   Divider,
@@ -10,6 +11,7 @@ import {
   Loader,
   PasswordInput,
   Stack,
+  Text,
   TextInput,
   VisuallyHidden
 } from '@mantine/core';
@@ -30,6 +32,7 @@ import { showLoginNotification } from '../../functions/notifications';
 import { useServerApiState } from '../../states/ServerApiState';
 import { useUserState } from '../../states/UserState';
 import { SsoButton } from '../buttons/SSOButton';
+import { errorCodeLink } from '../nav/Alerts';
 
 export function AuthenticationForm() {
   const classicForm = useForm({
@@ -341,6 +344,12 @@ export function RegistrationForm() {
           ))}
         </Group>
       )}
+      {!registration_enabled() && !sso_registration() && (
+        <Alert title={t`Registration not active`} color='orange'>
+          <Text>{t`This might be related to missing mail settings or could be a deliberate decision.`}</Text>
+          {errorCodeLink('INVE-W11')}
+        </Alert>
+      )}
     </>
   );
 }