- FillPicker component: 3 category tabs (Solid, Gradient, Image), gradient
subtype dropdown (Linear/Radial/Angular/Diamond), draggable gradient stop
bar, per-stop color/position/opacity editing with ScrubInput
- FillSection uses FillPicker instead of ColorPicker for full Fill editing
- Default gradient transforms for each subtype so renderer picks them up
- colorToRgba255/rgba255ToColor helpers in color.ts
- Custom SVG icons for fill type tabs (solid square, gradient fade)