Move a prospect between columns

Move a prospect to a different status column.

Every move is recorded with its source — manual, api or system —
so the card's activity trail can tell an integration's move from a
person's drag from an automatic promotion.

A move never changes what a partner IS. Send a column belonging to
another partner type — which is what the merged "All Prospects" view
does — and it resolves to the same position under this partner's own
type rather than reclassifying them.