Add ability to mark cards as "done"

[juliendemoutiez]

Implement functionality to allow users to mark cards as completed.

[clement-fouque]

I'm using Projects (Suite Numérique Territoriale) as a Kanban board. Great app 😉 !

It would be nice to be able to archive a card.

It might be a better solution as closing a card as when the card is done, we might want to keep it displayed for a period if time.