feat: check if first jellyfin user is admin (#635)

* feat: merge check if first jellyfin user is admin

re #610

* refactor(i18n): extract admin error message into en locale

---------

Co-authored-by: fallenbagel <98979876+Fallenbagel@users.noreply.github.com>

server/routes/auth.ts

@@ -276,6 +276,11 @@ authRoutes.post('/jellyfin', async (req, res, next) => {
     });
 
     if (!user && !(await userRepository.count())) {
+      // Check if user is admin on jellyfin
+      if (account.User.Policy.IsAdministrator === false) {
+        throw new Error('not_admin');
+      }
+
       logger.info(
         'Sign-in attempt from Jellyfin user with access to the media server; creating initial admin user for Overseerr',
         {
@@ -423,6 +428,11 @@ authRoutes.post('/jellyfin', async (req, res, next) => {
         status: 401,
         message: 'Unauthorized',
       });
+    } else if (e.message === 'not_admin') {
+      return next({
+        status: 403,
+        message: 'CREDENTIAL_ERROR_NOT_ADMIN',
+      });
     } else if (e.message === 'add_email') {
       return next({
         status: 406,