Radial gradients show a dashed extent ellipse: its handle across the bar
sets the aspect ratio, the ellipse elsewhere rotates it, and the dot inside
the centre ring drags the focal point (GradientGeom.focal) for an off-centre
radial. paint.setGradientGeom takes aspect (%) and focal ([x,y] | null), and
start/end may be left out; the focal point keeps its place in the ellipse as
the vector, aspect and object transform. It renders as a two-point radial,
exports and imports as SVG fx/fy and PDF two-point radial shadings, expands
to off-centre rings, and travels in gradient params and the native format.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>