Elevation and effects draft v0.2.0

Opacity, blur, drop shadow and shadow colors from the Figma library, and why no component uses them yet.

The Figma library brings opacity steps, blur radii, a drop-shadow number and five shadow colors (effect.shadow.1 to 5, a neutral step at 1 to 5 % opacity, in Colors / Mapped), all recreated as they are. No component uses an effect yet: translucency comes from color tokens, and surfaces stand apart by their color and border, not by elevation. This foundation owns the shadow colors, presents the primitives and states the rules any future effect follows.