fix: stop infinite scroll feedback when no more messages

Scroll handler now checks !hasMore to avoid calling fetchOlderMessages
when all messages are loaded. Previously the handler would fire on every
scroll event (since scrollTop stayed < 100), creating a .then() callback
loop that adjusted scroll position repeatedly, causing 'stuck' scrolling.

web/src/components/DMChat.tsx

@@ -156,6 +156,7 @@ export function DMChat() {
   const fetchMessages = useConversationStore((s) => s.fetchMessages);
   const fetchOlderMessages = useConversationStore((s) => s.fetchOlderMessages);
   const isLoadingOlder = useConversationStore((s) => s.isLoadingOlder);
+  const hasMore = useConversationStore((s) => id ? s.hasMoreByConversation[id] !== false : true);
   const isLoading = useConversationStore((s) => s.isLoading);
   const sendMessage = useConversationStore((s) => s.sendMessage);
   const fetchConversations = useConversationStore((s) => s.fetchConversations);
@@ -189,7 +190,7 @@ export function DMChat() {
 
   const handleScroll = useCallback(() => {
     const el = scrollContainerRef.current;
-    if (!el || !id || isLoadingOlder) return;
+    if (!el || !id || isLoadingOlder || !hasMore) return;
     if (el.scrollTop < 100) {
       const prevHeight = el.scrollHeight;
       fetchOlderMessages(id).then(() => {
@@ -198,7 +199,7 @@ export function DMChat() {
         });
       });
     }
-  }, [id, isLoadingOlder, fetchOlderMessages]);
+  }, [id, isLoadingOlder, hasMore, fetchOlderMessages]);
   const messages = id ? messagesByConv[id] || [] : [];
 
   useEffect(() => {