refactor(ui): refine Button primitive proportions and interaction hierarchy #878

Problem

The shared Button primitive feels too heavy in compact product surfaces. Its current height, padding, font weight, border, and filled neutral treatment create more visual weight than the action hierarchy requires.

Consumers should not compensate with local sizing or interaction styles.

Direction

Refine the shared Button size and neutral-variant matrix. Keep hover, active, focus, and disabled states distinct; verify compact CJK and English action groups; and update the Button and Interaction States stories as the visual specification.