[Docs] Collapse action buttons into menu on very small viewports

[techniq]

Reported on Twitter/X. Need to update Svelte UX and LayerChart

I'm thinking moving Github, Discord, and Twitter/X into a ... menu, but leaving Search and Theme selection top-level (if avaiable). We could move the Theme selector to the menu as well, if needed (but since it opens a modal, it might be nice to stay top-level).

Also planning to add a top-level locale/i18n selector at some point.

[techniq]

techniq/layerchart@01f791b