feat(skill): tailwind-syntax-utility-classes

Base utility-class vocabulary covering spacing, color, typography,
layout, flexbox, grid, sizing, border, background, and effects.
Includes v4 callouts for shadow scale insert (shadow-xs / shadow-2xs),
opacity-modifier slash syntax, shrink/grow rename, bg-linear-* rename,
text-ellipsis rename, important-modifier suffix position,
default border-color and ring-width changes.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: FreekHeijting