add server (Express app)

server/src/index.ts

@@ -0,0 +1,15 @@
+import dotenv from 'dotenv';
+import express, { Express } from 'express';
+
+dotenv.config();
+
+const app: Express = express();
+const port = process.env.PORT;
+
+app.get('/', (req, res) => {
+  res.send('Hello World!');
+});
+
+app.listen(port, () => {
+  console.log(`Server is running at ${port}`);
+});