Create a merge request from a card

GitLab's issue page has a button that creates a merge request and a branch for that issue. It is genuinely one of the better things about that page, and using it meant leaving GitGumbo.

Cards now have it. Create a merge request straight from the card, on GitLab boards, and it does what the provider's own button does — creates the branch, opens the merge request, and links it back to the issue so closing one closes the other.

It creates a draft. That is deliberate, and it was a real bug for a couple of days before it was fixed: a button that opens a review-ready merge request the moment you click it is a button that pings reviewers about work that does not exist yet. Drafts are the right default for something created at the start of a piece of work. Mark it ready when it is.

GitHub does not have an equivalent for this yet on our side, and the card knows that rather than offering a control that would fail.