Scaffold Express TODO API with GET /todos and GET /healthz

- Add package.json with express dependency and npm start script
- Add index.js: Express server on port 3000 with /todos and /healthz endpoints
- /todos returns 3 hardcoded todo objects {id, title, done}
- /healthz returns {ok: true}
- Update README.md with Run section

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

index.js

@@ -0,0 +1,22 @@
+const express = require('express');
+
+const app = express();
+const PORT = 3000;
+
+const todos = [
+  { id: 1, title: 'Buy groceries', done: false },
+  { id: 2, title: 'Walk the dog', done: true },
+  { id: 3, title: 'Read a book', done: false },
+];
+
+app.get('/healthz', (req, res) => {
+  res.json({ ok: true });
+});
+
+app.get('/todos', (req, res) => {
+  res.json(todos);
+});
+
+app.listen(PORT, () => {
+  console.log(`Server listening on http://localhost:${PORT}`);
+});