fix: instant scroll to bottom in chat instead of slow animation

Change Virtuoso followOutput from "smooth" to "auto" so new messages
appear instantly at the bottom rather than slowly animating into view.

src/components/ChatViewer.tsx

@@ -942,7 +942,7 @@ export function ChatViewer({
             ref={virtuosoRef}
             data={messagesWithMarkers}
             initialTopMostItemIndex={messagesWithMarkers.length - 1}
-            followOutput="smooth"
+            followOutput="auto"
             alignToBottom
             components={{
               Header: () =>