Refine UX for assistants (#13502)

<img width="1652" alt="image"
src="https://github.com/zed-industries/zed/assets/482957/376d1915-1e15-4d6c-966e-48f55f7cb249">


Release Notes:

- N/A

crates/zed/src/zed.rs

@@ -3181,7 +3181,7 @@ mod tests {
             project_panel::init((), cx);
             outline_panel::init((), cx);
             terminal_view::init(cx);
-            assistant::init(app_state.client.clone(), cx);
+            assistant::init(app_state.fs.clone(), app_state.client.clone(), cx);
             tasks_ui::init(cx);
             initialize_workspace(app_state.clone(), cx);
             app_state