google sign in with oauth 2.0. no more console errors or warnings

frontend/src/App.tsx

@@ -6,6 +6,7 @@ import Footer from './components/Footer';
 import Home from './pages/Home';
 import Login from './pages/Login';
 import Register from './pages/Register';
+import GoogleCallback from './pages/GoogleCallback';
 import ItemList from './pages/ItemList';
 import ItemDetail from './pages/ItemDetail';
 import EditItem from './pages/EditItem';
@@ -36,6 +37,7 @@ function App() {
           <Route path="/" element={<Home />} />
           <Route path="/login" element={<Login />} />
           <Route path="/register" element={<Register />} />
+          <Route path="/auth/google/callback" element={<GoogleCallback />} />
           <Route path="/items" element={<ItemList />} />
           <Route path="/items/:id" element={<ItemDetail />} />
           <Route path="/users/:id" element={<PublicProfile />} />