Update Agent panel to work with CloudUserStore (#35436)

This PR updates the Agent panel to work with the `CloudUserStore`
instead of the `UserStore`, reducing its reliance on being connected to
Collab to function.

Release Notes:

- N/A

---------

Co-authored-by: Richard Feldman <oss@rtfeldman.com>

crates/eval/src/instance.rs

@@ -221,6 +221,7 @@ impl ExampleInstance {
         let prompt_store = None;
         let thread_store = ThreadStore::load(
             project.clone(),
+            app_state.cloud_user_store.clone(),
             tools,
             prompt_store,
             app_state.prompt_builder.clone(),