v0.32.1: Sub-card counts after a move

A small fix to `v0.32.0’s card moves, found in testing the same day.

After moving a card that has sub-cards, the response reported sub_card_count: 0, even though the sub-cards had come along and were still attached. The target board showed the moved card without its sub-card progress until you reloaded the page. The Ticket API had the same gap and reported 0 for every card. All of these now report the real count.

The API documentation also spells out one thing that confused a tester: a moved card keeps its numeric id, but paths are per project. After a move, use the target project’s slug; paths under the old project return 404. The old card number (PRJ-12) keeps working, as before.