Docs: use arrow keys to select suggested search result

[platformer]

Description

The search bar in typst.app/docs displays suggested results as you type. It would be nice if you could navigate through these results with the up/down keys, and press enter to select one.

Use Case

This would make navigating the docs slightly easier. It would also bring it in line with other search bars across the web - I find myself trying to use the arrow keys whenever I revisit the docs after a while.

[MDLC01]

Also, the first result should be selected by default, so that you don't always have to press the arrow key or Tab ↹.