I need a straightforward proof-of-concept mobile app that lets users view and convert between major currencies. Because this is an initial concept on a tight budget, the scope is intentionally minimal: • Real-time exchange rates that I will update manually. Build a quick admin input (simple form, JSON, or even a local CSV reader) so I can change rates without touching the code. • Instant conversion calculator that reflects the most recent manual update. • Clean, uncluttered interface—just a rates screen and a converter screen. Cross-platform tools such as Flutter, React Native, or plain Android/iOS are all fine; choose whatever lets you move fastest. Deliver the runnable source, build instructions, and a brief note explaining how to update the rates. No user authentication or transaction logs are required at this stage, but I’d like the code structured so those features could be added later.