Initialize flavors (dev/stg/prod) in a Flutter project, or audit and fix an existing partial/broken flavor setup — Android (build.gradle.kts, AndroidManifest), iOS (xcconfig, xcscheme, Info.plist), Web (--dart-define WEB_FLAVOR workaround), multiple entry points (main_*.dart), IDE config (VSCode launch.json, Android Studio .idea/runConfigurations), and optional multi-project Firebase (flutterfire configure per flavor).
