Self-contained SKILL.md + path fix

What changed

SKILL.md is now fully self-contained — all reference content (token architecture, surface elevation, border progression, control tokens, dark mode, navigation context, card layouts, iconography, validation checks) is inlined. No external file reads needed.

This means the skill works across all agents (Claude Code, Cursor, Codex, Antigravity, and 35+ others) via the Vercel skills marketplace without any path resolution dependencies.

init.md uses relative paths instead of hardcoded ~/.claude/skills/ paths that broke when installed via the Claude plugin marketplace.

Fixes

• Closes #7 — Hardcoded paths in init.md break plugin installation

No prescriptive values

Reference content was merged as thinking and principles, not copy-paste CSS. No specific rgba values, shadow stacks, or pixel measurements that would encourage defaults over intentional choices.