fix: chat starts scrolled to bottom instead of visibly scrolling down

- Use onContentSizeChange to scroll after FlashList renders content
- Scroll without animation on initial load via needsInitialScroll ref
- Remove unreliable 100ms timeout scrollToEnd from message loading

apps/client/src/app/(tabs)/chat.tsx

@@ -64,11 +64,11 @@ const Chat = () => {
     string | undefined
   >();
   const [hasLoadedMessages, setHasLoadedMessages] = useState(false);
+  const needsInitialScroll = useRef(false);
 
   useEffect(() => {
-    const keyboardDidShow = Keyboard.addListener(
-      "keyboardDidShow",
-      scrollToEnd,
+    const keyboardDidShow = Keyboard.addListener("keyboardDidShow", () =>
+      scrollToEnd(),
     );
     return () => keyboardDidShow.remove();
   }, []);
@@ -90,7 +90,7 @@ const Chat = () => {
               await ChatService.getConversation(conversationId);
             const clientMessages = serverMessages.map(chatMessageToMessageData);
             addMessages(clientMessages);
-            scrollToEnd();
+            needsInitialScroll.current = true;
           }
         } catch (error) {
           console.error("Failed to load messages:", error);
@@ -102,9 +102,9 @@ const Chat = () => {
     }, [isAuthLoading, isAuthenticated, hasLoadedMessages]),
   );
 
-  const scrollToEnd = () => {
+  const scrollToEnd = (animated = true) => {
     setTimeout(() => {
-      listRef.current?.scrollToEnd({ animated: true });
+      listRef.current?.scrollToEnd({ animated });
     }, 100);
   };
 
@@ -277,6 +277,12 @@ const Chat = () => {
           keyExtractor={(item) => item.id}
           keyboardDismissMode="interactive"
           keyboardShouldPersistTaps="handled"
+          onContentSizeChange={() => {
+            if (needsInitialScroll.current) {
+              needsInitialScroll.current = false;
+              listRef.current?.scrollToEnd({ animated: false });
+            }
+          }}
           ListFooterComponent={
             isWaitingForResponse ? <TypingIndicator /> : null
           }