fix(ui): pin pagination dot dimensions to prevent flex-col stretch on mobile

[BilgeGates]

Closes #140

Summary

• Pagination dots were rendering as tall vertical bars on mobile inside flex-col containers (board theme preset and piece set pagers)
• Root cause: <button> elements inside a flex-col parent inherited align-self: stretch, overriding Tailwind h-*/w-* classes and making dots stretch to fill the container height
• Fix: pin all dot dimensions (width, height, min/maxWidth, min/maxHeight, borderRadius, padding, border) via inline style props — immune to any parent flex context
• Active dot restored to 20×8px accent pill; normal dots 8×8px; faded dots 6×6px

Test plan

• Open Export page → Board Style tab on mobile — pagination dots appear as horizontal row of circles/pill
• Open Export page → Board Style tab on desktop — same
• Piece set pager dots render correctly on both mobile and desktop
• Active dot shows as wider accent pill, inactive as small circles
• Clicking dots navigates pages correctly