fix(activity): wire onClearThread action to sidebar agents list

The sidebar notification list was not receiving the onClearThread callback,
so the clear button was never enabled. Wire the action from useActivityThreadActionBindings
down to the ActivityThreadListPane in the sidebar.

src/renderer/src/components/sidebar/SidebarAgentsList.tsx

@@ -82,7 +82,8 @@ export default function SidebarAgentsList({
     markAllThreadsRead,
     hasUnreadThreads,
     hasCompletedThreads,
-    handleClearCompleted
+    handleClearCompleted,
+    handleClearThread
   } = useActivityThreadActionBindings({
     visibleThreads,
     markAllReadThreads,
@@ -157,6 +158,7 @@ export default function SidebarAgentsList({
         onJumpToWorkspace={jumpToWorkspace}
         onMarkThreadRead={markThreadRead}
         onMarkThreadUnread={markThreadUnread}
+        onClearThread={handleClearThread}
         canJumpToWorkspace={canJumpToWorkspace}
         allowMarkUnreadWhenSelected
         showJumpAction={false}