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/t4-numbered-stat-strip.md

@@ -0,0 +1,14 @@
+### T4 · Numbered stat strip
+A horizontal strip of 3–5 stats (count + qualifier) running across one row. Tabular nums.
+*Use when:* you have multiple complementary metrics that work together.
+*Don't confuse with:* H4 Stat-led hero (which is one focal number, not several).
+
+```html
+<section class="stat-strip tnum">
+  <div><b>2.4M</b><span>users</span></div>
+  <div><b>99.97%</b><span>uptime</span></div>
+  <div><b>14</b><span>regions</span></div>
+</section>
+```
+
+---