add db class

src/client/frontend.tsx

@@ -0,0 +1,26 @@
+/**
+ * This file is the entry point for the React app, it sets up the root
+ * element and renders the App component to the DOM.
+ *
+ * It is included in `src/index.html`.
+ */
+
+import { StrictMode } from 'react';
+import { createRoot } from 'react-dom/client';
+import App from './App';
+
+const elem = document.getElementById('root')!;
+const app = (
+    <StrictMode>
+        <App />
+    </StrictMode>
+);
+
+if (import.meta.hot) {
+    // With hot module reloading, `import.meta.hot.data` is persisted.
+    const root = (import.meta.hot.data.root ??= createRoot(elem));
+    root.render(app);
+} else {
+    // The hot module reloading API is not available in production.
+    createRoot(elem).render(app);
+}