Undo/Redo system added to the layers panel (up to 10 steps back and forward)
Visibility toggle added to layers (kl0.png / kl1.png) — hide/show individual figures
Help button now supports 10 languages with a fixed language selector at the top
When the scene is empty, ab3.png blinks 3 times at the center of the screen
Old single-step undo button (sym7) removed and replaced with full undo/redo in layers