v0.3.0

Added

• LoadState<T, F> — a Loading/Success/Failure sealed state, plus a
  matching SkeletonContainer(state, onFailure, content) overload for it.
  Unlike the isFailure/dataOrNull overload, state's shape is fixed
  to LoadState in exchange for onFailure receiving a concretely typed
  failure payload with no cast required. Loading isn't special-cased by
  the overload — it's whatever state isn't Success or Failure, so
  the shimmer shows automatically with no extra branching needed.
  Demonstrated in the sample app via LoadStatePostCard.

Changed

• SkeletonContainer(state, dataOrNull, isFailure, onFailure, content)'s
  onFailure slot is now @Composable (S) -> Unit, receiving the failure
  state directly instead of requiring callers to re-derive it from the
  outer state.