fetch-data implementation

This tracks the implementation of the `fetch-data` module within Synchrotron.

`fetch-data` is a general purpose API layer that caches API results, keeps them current, and makes it easy for React components to access.

Start by locating the fetch-data module or its planned entry point in the Synchrotron repository and read how React components currently access API results. Identify the intended caching and freshness behavior before proceeding. Done means a documented, working API layer that caches results, keeps them current, and exposes them to React components.

Written by the indexing model from the issue text.