TrackPlaceBlockCommand::redo now homes the block's in point to the
placement target (capturing the original for undo): the Rust block
stores its position on the block, so a fresh clip that never had its
in point set always rendered at the timeline zero — the 'drops always
land at zero' bug. The original in point is captured on the first redo
and restored on undo, keeping the sync re-place round-trip exact. The
A/V drop test now asserts the clip lands at the drop frame.
Mike-Solar
877f577564