nav: inline search

[garrett]

It would be nice to pull the search feature into the navigation.

Doing so, however, would mean:

• Accommodating the space constraints of the header
• Including a shortened version of the results inline
• Lazy-loading the search index JSON, so it doesn't block the page

[nilaygit-10721]

can you assign me this issue?

[garrett]

If you want to work on the issue, work on the issue and send a PR. We don't assign people to the issues. This isn't on our radar as a priority, so please feel free to work on it if you'd like to. Thanks!