Fix TypeScript unused variable errors

server/index.ts

@@ -64,7 +64,7 @@ if (isProduction) {
   app.use(express.static(clientPath));
   
   // SPA fallback
-  app.get('*', (req, res) => {
+  app.get('*', (_req, res) => {
     res.sendFile(path.join(clientPath, 'index.html'));
   });
 }