Current topic: "Updating Screen State and Effects"
Topic summary: I am updating the `VehicleListScreen` composable to include the `showPaywallSheet` state and the `LaunchedEffect` that collects the `showPaywallSheet` signal from the ViewModel. I'm also removing the `LaunchPurchaseFlow` case from the effects collector as it's no longer used. These changes are essential for coordinating the visibility of the new `PaywallInfoSheet` with the ViewModel's logic.

Strategic Intent: Updating screen state and effects in VehicleListScreen.