feature: set up a simple server to serve the hello page

## Problem
We have a `greet` helper in `src/hello.js`, but nothing serves a hello page over HTTP yet.

## Expected
A minimal local server that serves a simple hello page (HTML or plain text) using the existing greet helper where appropriate.

## Actual
No server entrypoint or static page is wired up.

## Steps / acceptance
1. Add a small server (e.g. Node `http` or similar) that listens on a configurable port (default 3000).
2. `GET /` (or `/hello`) returns a hello page that includes a greeting.
3. Document how to run it in `README.md` or `docs/overview.md` (e.g. `npm start` / `node server.js`).
4. Keep the change small — no framework required unless already in the repo.

## Notes
Tier 1 `agent.mode` is `gh-aw`. Prefer org Copilot CLI billing (`copilot-requests: write`) over a personal `COPILOT_GITHUB_TOKEN`.

Start by reading src/hello.js to understand the existing greet helper, then inspect the repository's package configuration and README.md or docs/overview.md for current run conventions. Add a small server entrypoint with a configurable port and verify that GET / or /hello returns a greeting. Done means the server runs locally, the route serves the hello page, and the launch instructions are documented.

Written by the indexing model from the issue text.