Ctrl+Z undoes, Ctrl+Y and Ctrl+Shift+Z redo, caught in the capture
phase so a focused entry or spin never undoes only its own text; both
are in the header-bar menu too. The history keeps whole snapshots of
the project (currentProject() plus the immutable source list itself,
so stepping back never decodes again), compared by their JSON.
requestRender() notes every edit, and a step is committed once the
controls have been still for half a second. New and Open start the
history over once the project's images are in.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>