frontend: move routing logic from manage-backups to app.tsx

The main app component already has centralized routing logic in one
place that checks for empty device lists and routes accordingly.

Author: thisconnect

frontends/web/src/app.tsx

@@ -83,8 +83,13 @@ export const App = () => {
       return;
     }
     // if no devices are registered on specified views route to /
-    if (Object.keys(devices).length === 0 &&
-        currentURL.startsWith('/settings/device-settings/')) {
+    if (
+      Object.keys(devices).length === 0
+      && (
+        currentURL.startsWith('/settings/device-settings/')
+        || currentURL.startsWith('/manage-backups/')
+      )
+    ) {
       navigate('/');
       return;
     }

frontends/web/src/routes/device/manage-backups/manage-backups.tsx

@@ -16,7 +16,6 @@
  */
 
 import { useTranslation } from 'react-i18next';
-import { useNavigate } from 'react-router-dom';
 import { TDevices } from '@/api/devices';
 import { BackButton } from '@/components/backbutton/backbutton';
 import { Guide } from '@/components/guide/guide';
@@ -36,10 +35,8 @@ export const ManageBackups = ({
   devices,
 }: TProps) => {
   const { t } = useTranslation();
-  const navigate = useNavigate();
 
   if (!deviceID || !devices[deviceID]) {
-    navigate('/');
     return null;
   }