feat(notfound): add NotFound page with 404 handling and localization

src/App.jsx

@@ -18,6 +18,7 @@ import FederationInbox from './pages/FederationInbox';
 import FederatedRoomDetail from './pages/FederatedRoomDetail';
 import Calendar from './pages/Calendar';
 import OAuthCallback from './pages/OAuthCallback';
+import NotFound from './pages/NotFound';
 
 export default function App() {
   const { user, loading } = useAuth();
@@ -65,8 +66,8 @@ export default function App() {
         <Route path="/federation/rooms/:id" element={<FederatedRoomDetail />} />
       </Route>
 
-      {/* Catch all */}
-      <Route path="*" element={<Navigate to="/" />} />
+      {/* 404 */}
+      <Route path="*" element={<NotFound />} />
     </Routes>
   );
 }