The Transform panel had the link, but kept it in panel-local egui memory;
the Properties panel's Transform section and the Control bar had none, so
size changes there were never proportional.
The link is now the constrainProportions preference (prefs.get/prefs.set),
one toggle shared by the three places (transform::constrain_link), and every
W/H field passes it to object.setBounds as `proportional`.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>