Binder: Button/Card shape= and colors= (walk foundation.shape, accept ButtonDefaults.buttonColors) #307

From #172. Kotlin Button/Card take shape= / colors=. androidx.compose.foundation.shape is not walked, and the walker declines ButtonDefaults.buttonColors (B-1), so corner_radius and colour cannot be set from Python.
Completion: RoundedCornerShape(...) and ButtonDefaults.buttonColors(...) are reachable from Python, and a compose fixture render test shows a Button and a Card with a custom shape and colours. Red before the fix.