feat(web): sprint1 ui core with global toasts and improved chat layout

web/src/app/App.tsx

@@ -1,4 +1,5 @@
 import { useEffect } from "react";
+import { ToastViewport } from "../components/ToastViewport";
 import { AuthPage } from "../pages/AuthPage";
 import { ChatsPage } from "../pages/ChatsPage";
 import { useAuthStore } from "../store/authStore";
@@ -27,5 +28,10 @@ export function App() {
   if (!accessToken || !me) {
     return <AuthPage />;
   }
-  return <ChatsPage />;
+  return (
+    <>
+      <ChatsPage />
+      <ToastViewport />
+    </>
+  );
 }