apparently offset on y axis is smaller now?

honestly i don't understand why they weren't 0,0 to start with. there
must be some layout shifts i don't understand yet. gotta figure that out
someday.

- set theme select value after DOMConentLoaded
- refactor: move inline `onchange` to `<script>`

- remove inject-footnotes.js, use a partial that receives `.Content` and
does the injection statically
- use a `utils/render` partial, as custom "render hook"
- reuse `content` partial for all pages