Improve design system output with Unicode borders, ANSI color swatches, extended palette, and dark/light mode

Upgrade the design system terminal output from basic ASCII to Unicode box-drawing characters,
add ANSI true color swatches with graceful fallback, expand the color palette from 5 to 10
colors (Primary, On Primary, Secondary, Accent, Background, Foreground, Muted, Border,
Destructive, Ring) with CSS variable names, and surface Light/Dark mode support from styles.csv.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>