Addresses the round-1 review on PR #885:
- Preserve `done` across a cross-board move. The internal card-update route
(the only one that works cross-board — the board/stack-scoped route 404s for
a card not already on that board) does not accept a done value, so a "done"
card is re-marked done after the move. Deck stamps the current time there, so
the original timestamp isn't preserved — documented as a route limitation.
(`archived` is already preserved: CardService only mutates it when sent.)
- Validate that target_stack_id is on target_board_id before moving, so the
parameter is load-bearing and a mismatch fails loudly instead of misreporting.
- Skip the same-board guard's get_stacks round-trip on a same-stack reorder.
- Add unit coverage (done-restore call, destination validation, same-stack
skip) and integration coverage (done preservation, target-board mismatch).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
