title: Get observable notebook metadata
body: <p>I'm trying to build a "preview card" to link an observable notebook:
  - preview image
  - title 
  - description</p>
  
  <p>is there an api that can be used to do this? I have tried to use <code>https://api.observablehq.com/document/{user}/{notebook}@latest</code>, but it is referrer protected.</p>
  
  <p>Also tried fetching the html and parsing the meta headers, but can only get an opaque response via <code>no-cors</code>.</p>
  
  <p>This implementation is a static website that will be linking directly to the notebooks, so a server to parse the page is off the table.</p>