* picture.change: keep the width and take the new picture's aspect ratio
Change Picture swapped only the media key, so a replacement of another
shape was stretched into the old frame (a revised figure came out ~2%
taller in a real manuscript). Keep the display width, set the height
from the new picture's pixel size, and drop the old crop, which
described the old picture. Regression test included.
* docs: progress log and parity entries for picture-change-aspect
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Co-authored-by: Martin Ball <martin.ball@ucscaregroup.co.uk>
