Apply up to 100 partial card updates in one transaction

All-or-nothing batch update. Each item is { "id": … } plus any fields the single-card PATCH accepts, with identical semantics (present = apply, null = clear, absent = leave alone). Column / priority / assignee changes are recorded to each card's activity log. One invalid item or missing card fails the whole batch and the error names the offending index. Bulk requests never send notification emails. Body limit 1 MiB.