Fix/active session tracking (#176)

* refactor(chat): enhance scroll management

Add bottom detection with epsilon tolerance for precise positioning
Introduce pending anchor restoration for seamless session switching
Include active turn anchor and spacer height in message store

packages/ui/src/components/chat/MessageList.tsx

@@ -19,7 +19,7 @@ interface MessageListProps {
     hasMoreAbove: boolean;
     isLoadingOlder: boolean;
     onLoadOlder: () => void;
-    scrollToBottom?: (options?: { instant?: boolean; force?: boolean }) => void;
+    scrollToBottom?: (options?: { instant?: boolean; force?: boolean; clearAnchor?: boolean }) => void;
     pendingAnchorId?: string | null;
 }