Challenge 3: Collecting UiState in a Composable — Solution

@Composable
fun TodoScreen(viewModel: TodoViewModel = viewModel()) {
    val uiState by viewModel.uiState.collectAsStateWithLifecycle()

    Column(modifier = Modifier.padding(16.dp)) {
        if (uiState.isLoading) {
            Text(text = "Loading...")
        } else {
            uiState.items.forEach { item ->
                Text(text = item)
            }
        }

        Spacer(modifier = Modifier.height(12.dp))

        Button(onClick = { viewModel.addItem("New task ${uiState.items.size + 1}") }) {
            Text("Add Item")
        }
    }
}

Notes:
- val uiState by viewModel.uiState.collectAsStateWithLifecycle() collects
  the WHOLE TodoUiState object as a single piece of Compose state — both
  uiState.isLoading and uiState.items come from that one collected value,
  never out of sync with each other.
- The if (uiState.isLoading) / else branch renders completely different
  content depending on the state's isLoading flag — this is the payoff
  of the single-UiState-per-screen pattern from the chapter: one clean
  branch, rather than juggling several independent booleans and lists
  that could theoretically disagree with each other.
- uiState.items.forEach { item -> Text(text = item) } uses Kotlin
  Fundamentals Chapter 6's forEach to render one Text per item — since
  addItem() replaces the whole TodoUiState (Challenge 2), tapping the
  button triggers recomposition and the new item appears in the list
  automatically.