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/s2-hanging.md

@@ -0,0 +1,13 @@
+### S2 · Hanging
+Heading floats above the section in negative space; no border, no rule.
+*Use when:* the content has a quiet, room-to-breathe energy.
+*Don't confuse with:* S3 Sticky-pinned (which moves with scroll).
+
+```html
+<header class="head-hang">
+  <h2>…</h2>
+</header>
+```
+```css
+.head-hang { padding-block: var(--space-3xl) var(--space-xl); }
+```