sidebar: navigate to project in Project Manager using slug

The Home icon in the PROJECT panel now navigates to /projects/{slug}
instead of /projects/{id}. This opens Project Manager with the
project already selected and displayed.

gadget-code/frontend/src/pages/ChatSessionView.tsx

@@ -1257,7 +1257,7 @@ export default function ChatSessionView() {
             </h3>
             <button
               title="Project Manager"
-              onClick={() => navigate(`/projects/${projectId}`)}
+              onClick={() => navigate(`/projects/${project?.slug}`)}
               className="text-text-muted hover:text-text-primary transition-colors"
             >
               <svg className="w-4 h-4" fill="none" viewBox="0 0 24 24" stroke="currentColor">