Add an explicit card completion state

[bionicman]

✨ Feature Request

Is your feature request related to a problem? Please describe.

Kan currently has due dates and completed checklist items, but a card itself cannot be marked complete. Moving a finished card to another list can express workflow state, but it is not always the same thing: teams may keep completed and incomplete cards together, and due dates should not keep presenting a finished card as overdue.

This also loses useful state when moving from Trello, where cards can have dueComplete independently of their due date.

Describe the solution you'd like

Add a boolean completion state to cards with:

• an accessible completion toggle beside the card title;
• a compact completed indicator on cards in the board view;
• completed due dates shown as completed instead of overdue;
• Complete and Incomplete options under a Card status board filter;
• activity entries and webhook change data when the state changes;
• the same read-only indication on public boards;
• Trello import support for both due and dueComplete.

New cards should remain incomplete by default. Completion should be independent of lists, checklists and due dates, so existing workflows keep behaving as they do today.

Describe alternatives you've considered

Treating a particular list as "done" would make completion depend on a board's layout and would require board-level configuration. Inferring completion from checklists would not work for cards without checklists or for partially completed work. Reusing the due date alone would also couple two separate pieces of state.

Additional context

I am migrating teams from Trello and have already exercised this model in our Kan fork against imported data. Keeping completion explicit preserved the existing workflow while making completed, overdue and unscheduled cards unambiguous. I can share the implementation for review later if the direction fits the project.

Completed and incomplete cards on the same board:

Completion in card detail:

Filtering by card status:

Mobile

Implementation ideas (optional)

A completed boolean on the card keeps the model small. The existing card update path can own authorization, activity creation and webhook emission, and the board query can apply the completion filter alongside its current filters. The Trello importer can map dueComplete directly without adding Trello-specific behavior to the card model.

Would you like to work on this feature?

• Yes, I'd like to help implement this feature
• No, I'm just suggesting the feature