Ability to check a task from preview mode

### What

The purpose of a checklist is to check things off.

I often create checklists within notes that contain added context, such as markdown images etc.

These notes are mostly viewed in preview mode. Checkboxes are rendered in preview mode, but it would be amazing if we could also mark any task as done when in preview mode.

### Why

Currently I find myself switching to editing mode to try and find the checkbox on the page so I can check the box, after which I need to switch back to the preview mode, which is an annoying journey and not at all 'simple'.

Start by locating the preview-mode rendering for checkboxes and the existing edit-mode task toggle. Confirm the behavior with a rendered checklist in preview mode; done means tasks can be marked complete there without leaving preview mode.

Written by the indexing model from the issue text.