zuhairahmed-3/mern-weather ? reverse-engineered prompt

Build me a small weather app where someone can type a US zip code, a city name, or both, and see the current temperature, conditions, and wind. If both are entered, use the zip code first, but if that zip is invalid and a city was also entered, fall back to the city and show a helpful message.

I want guests to be able to look up places without signing in, but only logged in users should have their searches saved to their account and show up again when they come back. Please make it work without any paid weather API key, using free public sources for weather, geocoding, and US zip lookup.

Keep it simple and clean, with a basic modern UI and a small API. If MongoDB is available, save accounts and searches there, and if not, let it still work in memory so the app does not break.