fix: strategy studio black screen on create and remove stale benefit3 ref

- Add missing configResponse.ok check in handleCreateStrategy to prevent
  rendering with invalid config data when API fails
- Remove deleted benefit3 translation key reference from LoginRequiredOverlay

web/src/components/auth/LoginRequiredOverlay.tsx

@@ -23,7 +23,6 @@ export function LoginRequiredOverlay({ isOpen, onClose, featureName }: LoginRequ
   const benefits = [
     tr('benefit1'),
     tr('benefit2'),
-    tr('benefit3'),
     tr('benefit4'),
   ]