Add GET /hello endpoint returning plain-text greeting

[Copilot]

The issue requested explicit support for a hello response. This PR adds a dedicated endpoint to serve that response directly from the Express app.

• Problem addressed

  • Add a canonical HTTP route that returns hello.

• Changes

  • Added a new route in index.js:
    • GET /hello → hello (plain text)
  • Kept existing routes and middleware wiring unchanged to avoid side effects.

• Implementation snippet

  app.get("/hello", (req, res) => {
    res.send("hello");
  });