a11y: comprehensive WCAG 2.1 Level AA accessibility audit

- Add skip-to-main-content link and main content ID target
- Add prefers-reduced-motion media queries for all animations
- Enhance visible focus indicators (2px offset, high-contrast ring)
- Replace ~160 text-surface-500 instances with text-surface-600/dark:text-surface-400
  for 4.5:1+ contrast ratio compliance
- Add aria-hidden="true" to ~30+ decorative SVG icons across sidebars/widgets
- Convert facepile containers from div to semantic ul/li with role="list"
- Add aria-label to icon-only buttons (share, sort controls)
- Add sr-only labels to form inputs (webmention, search)
- Add aria-live="polite" to dynamically loaded webmentions
- Add aria-label with relative+absolute date to time-difference component
- Add keyboard handlers (Enter/Space) to custom interactive elements
- Add aria-label to nav landmarks (table of contents)
- Fix modal focus trap and dialog accessibility
- Fix lightbox keyboard navigation and screen reader announcements

Confab-Link: http://localhost:8080/sessions/edb1b7b0-da66-4486-bd9c-d1cfa7553b88

_includes/components/cv-builder.njk

@@ -74,7 +74,7 @@
       {% endif %}
       {# Contact details — location, organization, website, email, PGP #}
       {% if cvLocality or cvCountry or cvOrg or cvUrl or cvEmail or cvKeyUrl %}
-      <div class="flex flex-wrap gap-x-4 gap-y-1 mt-4 text-sm text-surface-500 dark:text-surface-400">
+      <div class="flex flex-wrap gap-x-4 gap-y-1 mt-4 text-sm text-surface-600 dark:text-surface-400">
         {% if cvLocality or cvCountry %}
         <span>{% if cvLocality %}{{ cvLocality }}{% endif %}{% if cvLocality and cvCountry %}, {% endif %}{% if cvCountry %}{{ cvCountry }}{% endif %}</span>
         {% endif %}
@@ -160,7 +160,7 @@
 
 {# Last Updated #}
 {% if cv.lastUpdated %}
-<p class="text-sm text-surface-500 text-center mt-8">
+<p class="text-sm text-surface-600 dark:text-surface-400 text-center mt-8">
   Last updated: <time class="font-mono text-sm" datetime="{{ cv.lastUpdated }}">{{ cv.lastUpdated | date("PPP") }}</time>
 </p>
 {% endif %}