Node HTTP server for notes with health, list, add, stats endpoints

Build a small Node HTTP server in server.js with no dependencies, listening on the port given by the PORT environment variable. GET /health returns {"ok": true}. GET /api/notes returns the notes kept in notes.json in the working directory (an empty list at first), and POST /api/notes adds a note with a title and a body, refusing a missing title or body with 400 and a JSON error. GET /api/stats returns {"notes": <number of notes>}. Write a README that explains how to start the server and documents every route with an example. In the README every URL must be written as http://localhost:PORT with the literal word PORT, because the port is chosen at start-up; the README must not contain any numeric port.

Extend the existing notes server without breaking its routes. Add DELETE /api/notes/:id, which removes the note and answers 204, or 404 with a JSON error for an unknown id; notes need a stable id, so give every note an id when it is created and keep existing notes working. GET /api/stats gains "oldest" and "newest", the creation times of the oldest and newest notes, or null when there are none. Update the README: document DELETE /api/notes/:id and the new stats fields with examples, keep every URL written as http://localhost:PORT with the literal word PORT, and end the README with a "Changelog" section listing, as bullet points, each route this change added or modified.

Extend the existing notes server without breaking its routes. Add PATCH /api/notes/:id, which updates a note's title and/or body and answers the updated note, 400 with a JSON error when the title is present but empty, and 404 with a JSON error for an unknown id. Make GET /api/notes accept an optional q query parameter that returns only the notes whose title or body contains that text, case-insensitively; without q it returns every note as before. Update the README: document PATCH /api/notes/:id and the q parameter with examples, keep every URL written as http://localhost:PORT with the literal word PORT, and add both changes to the existing Changelog section as bullet points.

Extend the existing notes server without breaking its routes. Add GET /api/notes/:id, which answers the note with that id, or 404 with a JSON error for an unknown id. Make GET /api/notes accept an optional sort query parameter: sort=newest returns the notes newest first, sort=oldest oldest first, any other value answers 400 with a JSON error, and without sort the order is unchanged; it must still combine with the existing q filter. Update the README: document GET /api/notes/:id and the sort parameter with examples, keep every URL written as http://localhost:PORT with the literal word PORT, and add both changes to the existing Changelog section as bullet points.