Challenge 2: State and Recomposition — Solution

@Composable
fun Counter() {
    var count by remember { mutableStateOf(0) }

    Column(modifier = Modifier.padding(16.dp)) {
        Text(text = "Count: $count", fontSize = 20.sp)
        Row {
            Button(onClick = { count-- }) {
                Text("-")
            }
            Spacer(modifier = Modifier.width(8.dp))
            Button(onClick = { count++ }) {
                Text("+")
            }
        }
    }
}

@Preview(showBackground = true)
@Composable
fun CounterPreview() {
    Counter()
}

Notes:
- var count by remember { mutableStateOf(0) } uses property delegation
  (Kotlin Intermediate Chapter 4) — count can be read and reassigned
  like a normal var (count++, count--), while Compose secretly tracks
  every place that reads it.
- Tapping either Button runs its onClick lambda, which reassigns count.
  Compose then automatically recomposes the Text(text = "Count: $count")
  line specifically, since it's the composable that reads count — the
  Buttons and Row structure themselves don't need to re-run.
- remember { } (without rememberSaveable) means count resets to 0 if
  the Activity is recreated (e.g. on rotation, per Course 1 Chapter 2) —
  rememberSaveable is the variant that survives that, mentioned in the
  chapter but not required for this challenge.