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/f5-annotated-screenshot.md

@@ -0,0 +1,11 @@
+### F5 · Annotated screenshot
+A product capture sits centre-stage with arrows or short labels pointing to UI details.
+*Use when:* the product UI itself is the explanation.
+*Don't confuse with:* F2 Sticky-scroll (which uses multiple screenshots in sequence).
+
+```html
+<figure class="annotated">
+  <img src="" />
+  <span class="callout" style="--x:60%; --y:30%;">→ assigns automatically.</span>
+</figure>
+```