refactor: isolate Netlify dependencies

This boilerplate shouldn't be dependent on specific deploy environments. For now, it's tuned to my specific needs, and `netlify` is incidentally my deploy environment of choice at this moment.

Changes needed are:
- [ ] Abstract away dependency on `netlify/blobs` for storage.
- [ ] Provide an example on migrating to `vercel` — or support both deploy targets by default.