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>

README.md

@@ -1,3 +1,14 @@
 # todo-app
 
-Throwaway playground for the agent-coding-empire v0. Built end-to-end by autonomous dev agents from PM-authored issues.
+Throwaway playground for the agent-coding-empire v0. Built end-to-end by autonomous dev agents from PM-authored issues.
+
+## Run
+
+```bash
+npm install && npm start
+```
+
+The server starts on port 3000.
+
+- `GET /todos` — returns a JSON array of todo items
+- `GET /healthz` — returns `{ "ok": true }`