Theme code blocks in posts; a11y fixes from impeccable audit

- Dark velvet pre/code styling + Westgate hljs syntax palette for post
  content and composer preview (markdown plugin's light hljs theme was
  rendering white blocks)
- Visible focus ring on mobile drawer search (was outline: 0 with no
  replacement)
- Placeholder contrast raised to pass 4.5:1; tagsinput placeholder now
  reuses the token instead of $gray-500
- prefers-reduced-motion block zeroing transitions/animations
- Fix stray </li> closing a <div> in quick-search-results.tpl

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

scss/westgate/_responsive.scss

@@ -54,3 +54,13 @@
 		box-shadow: 0 -8px 20px rgba(0, 0, 0, 0.28);
 	}
 }
+
+@media (prefers-reduced-motion: reduce) {
+	*,
+	*::before,
+	*::after {
+		animation-duration: 0.01ms !important;
+		animation-iteration-count: 1 !important;
+		transition-duration: 0.01ms !important;
+	}
+}