Add explicit /hi greeting endpoint

[Copilot]

The issue asks for a minimal implementation of a hi requirement. This PR adds a dedicated endpoint that returns a plain-text hi response without changing existing routes or middleware behavior.

• What changed

  • Added a new GET /hi route in index.js.
  • The route returns a simple plain-text response: hi.
  • Existing endpoint structure and routing order were preserved.

• Endpoint behavior

  app.get("/hi", (req, res) => {
    console.log(`${new Date()} ${req.method} ${req.path}`);
    res.send("hi");
  });