Add due date, self-assign and filter keyboard shortcuts

Which part of the project does this feature apply to?

Frontend

What would you like?

Add Trello-style keyboard shortcuts for faster card and filter management on boards. Proposal:

Card under the cursor:

• D — open the due date editor (project cards, where due date is available)
• Space — join / leave the card (toggle self-assignment)

Board-level:

• Q — toggle the "cards assigned to me" filter
• X — clear all filters (members, labels and search)

Why is this needed?

These mirror the familiar Trello shortcuts (trello.com/shortcuts), lowering the entry barrier for users migrating from Trello.

Other information

I have a working implementation ready to submit as a PR — happy to adjust the key bindings or behavior based on maintainers' feedback