Support nightly export of todo canvas

[juh2600]

Depends on #2, but also needs investigation to figure out whether/how to export a canvas from Obsidian in an automated fashion. Maybe they have a command line or a plugin for this.

[juh2600]

Doesn't seem like automated exports are a thing, but also, the format is an open standard and looks pretty straightforward. It's also apparently very young, only a few months old in the wild. It might be feasible to just build a little interpreter for this format directly for the web, which would 1/ be useful to the general public 2/ sidestep dependence on #2.