Gradient tool handles (a drawn vector's start and end, the end handle and the moved start) snap to anchors, edges
and smart guides, with the guide overlays; Shift constrains to 45° steps from the Constrain Angle preference
(`ToolContext::constrain_angle`, `constrain_angle_from` in geom). Double-clicking a toolbar button runs the new UI
command `tool.options {tool}`: the Gradient tool opens the Gradient panel, the Eyedropper opens Eyedropper Options
(`eyedropper.setOptions {appearance?, transparency?}`, which `appearance.copyFrom` honours and its params override).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>