feat: add hallmark design skill

Anti-AI-slop design skill (greenfield pages, audits, redesigns, design
extraction from URLs/screenshots) -- installed and validated in an
earlier session, was sitting untracked. Full reference library:
components, macrostructures, themes, genres, verbs (audit/redesign).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

skills/hallmark/references/components/c3-typographic-link.md

@@ -0,0 +1,8 @@
+### C3 · Typographic link
+Just a word, an arrow, and a 1-px underline. No box, no fill.
+*Use when:* the page is editorial / Long Document; CTAs should not shout.
+*Don't confuse with:* C1 Outlined chip (which is bordered).
+
+```html
+<a class="link">Read the case study →</a>
+```