fix(ui): wrap agent ID in span for CSS truncate ellipsis

SidebarMenuButton applies truncate via [&>span:last-child]:truncate,
so the text must be in a <span> rather than a bare text node to get
overflow-hidden + text-ellipsis + whitespace-nowrap.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/web/app/components/hub-sidebar.tsx

@@ -79,7 +79,7 @@ export function HubSidebar() {
                       onClick={() => setActiveAgentId(agent.id)}
                       className="font-mono text-xs flex-1 min-w-0"
                     >
-                      {agent.id}
+                      <span>{agent.id}</span>
                     </SidebarMenuButton>
                     <button
                       onClick={() => {