🐛(frontend) handle 401 responses when syncing user preferences

401 responses were not handled by the user preferences sync, which
could leave the app in an inconsistent state when the session had
expired.

Handle the 401 case explicitly and report the error through the
telemetry module so it stays visible without crashing the flow.

src/frontend/src/features/auth/api/useSyncUserPreferencesWithBackend.tsx

@@ -6,6 +6,8 @@ import { queryClient } from '@/api/queryClient'
 import { updateUserPreferences } from './updateUserPreferences'
 import { convertToBackendLanguage } from '@/utils/languages'
 import { useUser } from './useUser'
+import { ApiError } from '@/api/ApiError.ts'
+import { reportError } from '@/features/analytics/telemetry'
 
 /**
  * Hook that synchronizes user browser preferences (language, timezone) with backend user settings.
@@ -42,6 +44,11 @@ export const useSyncUserPreferencesWithBackend = () => {
       }
     }
 
-    syncBrowserPreferencesToBackend()
+    syncBrowserPreferencesToBackend().catch((error) => {
+      if (error instanceof ApiError && error.statusCode === 401) return
+      reportError('generic_failure', error, {
+        context: '[useSyncUserPreferencesWithBackend] Failed to sync:',
+      })
+    })
   }, [i18n.language, isLoggedIn, user, mutateAsync])
 }