Reorder cards within a column

Dragging a card between columns has always moved it between stages. Dragging a card within its column now sets its position there, on GitLab boards, and the order is written back rather than being a local rearrangement that the next sync undoes.

There is a keyboard and switch-accessible path to the same result, and it is not a drag with a keyboard bolted on. Drag is a poor primitive to emulate: it needs pointer precision and continuous input, and the accessible version of "pick this up, move it, put it down" is usually a menu that names the destination rather than a simulation of the gesture. So card placement and column reordering both have a real menu-driven route, which is quicker than dragging even if you have no reason to need it.

One thing found while building this and worth recording: our GitLab reorder call was sending the inverted direction, so every drag wrote the opposite placement to the one performed. That is fixed. Reordering is also the kind of change that does not always register as an update on the provider's side, so the ordering is reconciled on a slower schedule underneath the fast path.