feat(web): port chat UI — model selector, keybindings, thinking display, styled header

apps/web/src/components/layout/topbar.tsx

@@ -1,11 +1,16 @@
 'use client';
 
-import { useRouter } from 'next/navigation';
+import { usePathname, useRouter } from 'next/navigation';
 import { useSession, signOut } from '@/lib/auth-client';
 
 export function Topbar(): React.ReactElement {
   const { data: session } = useSession();
   const router = useRouter();
+  const pathname = usePathname();
+
+  if (pathname.startsWith('/chat')) {
+    return <></>;
+  }
 
   async function handleSignOut(): Promise<void> {
     await signOut();