refresh: Modernize to ESM, drop pre-installed Sentry deps

.gitignore

@@ -1 +1,5 @@
-node_modules
+node_modules
+.env
+.env.local
+.DS_Store
+npm-debug.log*

README.md

@@ -1,5 +1,31 @@
-# Sample Backend Repo for Sentry Tracing Tutorial
+# Sentry Getting-Started Tutorial — Backend Sample
 
-quickstart: `npm install && node server.js`
+A small Express API used by the [Sentry getting-started tutorial](https://docs.sentry.io/product/sentry-basics/getting-started-tutorial/). It serves four product endpoints consumed by the companion [React frontend](https://github.com/getsentry/tracing-tutorial-frontend), plus a `/products/debug-sentry` route that throws an error you'll wire up to Sentry during the tutorial.
 
-Refer to URL_HERE for more info.
+## Run it
+
+Requires **Node 18+**.
+
+```bash
+npm install
+npm start
+```
+
+The server runs at [http://localhost:3001](http://localhost:3001).
+
+## Endpoints
+
+| Path | What it does |
+|---|---|
+| `GET /` | Hello message |
+| `GET /products` | Lists the products route |
+| `GET /products/kitten-mittens` | Returns product info |
+| `GET /products/doggles` | Returns product info |
+| `GET /products/clown-shoes` | Returns product info |
+| `GET /products/nonfat-water` | Returns product info |
+| `GET /products/debug-sentry` | Throws a sample error |
+| `GET /img/*` | Static product images |
+
+## Tutorial steps
+
+Follow the [tutorial](https://docs.sentry.io/product/sentry-basics/getting-started-tutorial/) for the full flow.