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/s1-left-margin-numbered.md

@@ -0,0 +1,15 @@
+
+### S1 · Left-margin numbered
+A narrow left column holds `01 — LABEL.`; the wide right column holds the heading and content.
+*Use when:* the page is editorial / specimen.
+*Don't confuse with:* S5 Bottom-anchored (which puts the label *under* the section).
+
+```html
+<header class="head-margin">
+  <p class="num-label">01 — Foundations</p>
+  <h2>…</h2>
+</header>
+```
+```css
+.head-margin { display: grid; grid-template-columns: 10rem 1fr; gap: var(--space-xl); align-items: baseline; }
+```