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/f3-tabular-spec-sheet.md

@@ -0,0 +1,11 @@
+### F3 · Tabular spec sheet
+Each row is a feature; columns hold name, value, footnote. Hairline rules between rows. Tabular numerics.
+*Use when:* features compare quantitatively.
+*Don't confuse with:* F1 Bento (which is non-tabular and visually rhythmic).
+
+```html
+<table class="spec-sheet tnum">
+  <tr><th>Latency</th><td>p99 &lt; 50 ms</td><td class="muted">measured externally</td></tr>
+  <tr>…</tr>
+</table>
+```