agent: Make ToolWorkingSet an Entity (#28757)

Motivation is to emit events when enabled tools change, want to use this
in #28755

Release Notes:

- N/A

crates/agent/src/profile_selector.rs

@@ -86,7 +86,7 @@ impl ProfileSelector {
 
                             thread_store
                                 .update(cx, |this, cx| {
-                                    this.load_profile_by_id(&profile_id, cx);
+                                    this.load_profile_by_id(profile_id.clone(), cx);
                                 })
                                 .log_err();
                         }