Open a chat at the newest message

The size-keyed follow effect animated from the very top on first
composition — a tour of the history before landing. A Unit-keyed instant
jump runs first; the animated follow keeps handling arrivals.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app/src/main/kotlin/io/flamenet/messenger/app/ChatScreens.kt

@@ -1263,6 +1263,10 @@ fun ColumnScope.ChatScreen(
     var draft by remember { mutableStateOf("") }
     val listState = rememberLazyListState()
 
+    // Open AT the newest message — a jump, not a tour of the history.
+    LaunchedEffect(Unit) {
+        if (chat.lines.isNotEmpty()) listState.scrollToItem(chat.lines.lastIndex)
+    }
     // Follow the conversation as it grows. Without this a reply arrives
     // off-screen and the app looks like it did nothing.
     LaunchedEffect(chat.lines.size) {