NetworkStatusBanner class

Thin banner pinned to the top of the screen, shown while connected is false (e.g. so a silent cloud-save failure isn't a confusing "why didn't my progress save?" moment).

Pure presentation: it takes network state from the caller — either a plain connected bool (caller flips it, same "caller owns the state" convention as LoadingOverlay) or, via NetworkStatusBanner.stream, a Stream<bool> — and never reaches for a connectivity package itself, so the kit gains no new dependency and the app decides its own signal source.

Built entirely from implicit animations (AnimatedSize/AnimatedOpacity) rather than an owned AnimationController — nothing to leak: both stop ticking on their own once the target value is reached.