agent2: Token count (#36496)

Release Notes:

- N/A

---------

Co-authored-by: Agus Zubiaga <agus@zed.dev>

crates/agent_ui/src/agent_diff.rs

@@ -1526,6 +1526,7 @@ impl AgentDiff {
                 self.update_reviewing_editors(workspace, window, cx);
             }
             AcpThreadEvent::TitleUpdated
+            | AcpThreadEvent::TokenUsageUpdated
             | AcpThreadEvent::EntriesRemoved(_)
             | AcpThreadEvent::ToolAuthorizationRequired
             | AcpThreadEvent::Retry(_) => {}