Flutter Config

Sets up Flutter app flavors the right way: one main.dart entry point, environment config via dart-define-from-file JSON files, and proper platform setup for iOS and Android. You get three flavors out of the box (dev, staging, prod) with separate Firebase projects, bundle IDs, and API endpoints. The approach is cleaner than the old multi-entry-point pattern and keeps secrets out of your JSON configs. If you're tired of hardcoded URLs or juggling environment variables across build scripts, this gives you a reproducible structure that works locally and in CI without the usual flavor setup headaches.