feat(ui): Inter + design-system preview page (#10)

frontend/src/main.jsx

@@ -9,7 +9,9 @@ import Unsubscribe from './pages/Unsubscribe.jsx';
 import FolderView from './pages/FolderView.jsx';
 import SearchResults from './pages/SearchResults.jsx';
 import Layout from './components/Layout.jsx';
+import DesignSystem from './pages/DesignSystem.jsx';
 import { ToastProvider, TooltipProvider } from './components/ui';
+import '@fontsource-variable/inter';
 import './index.css';
 import './styles.css';
 
@@ -30,6 +32,7 @@ ReactDOM.createRoot(document.getElementById('root')).render(
           <Route path="unsubscribe" element={<Unsubscribe />} />
           <Route path="folder/:slug" element={<FolderView />} />
           <Route path="search" element={<SearchResults />} />
+          <Route path="design" element={<DesignSystem />} />
         </Route>
 
             <Route path="*" element={<Navigate to="/" replace />} />