App startup and bootstrap

Enforces a fixed main() cold-launch order — crash-log sink + FlutterError.onError + PlatformDispatcher.onError installed BEFORE any code that can throw, settings/theme read before runApp so the first frame paints correct, real infra constructed in a composition-root bootstrap() and injected via ProviderScope overrideWithValue over throwing placeholder providers, non-blocking warm-up deferred to addPostFrameCallback, exactly two error handlers with NO runZonedGuarded, ProviderException unwrapped before logging, and a WidgetsBindingObserver that flushes durable state on background/resume. Use when editing lib/main.dart, main_<flavor>.dart, bootstrap.dart or app.dart, reorde…