fix: align templates with wireframe styling

- Fix article header tag borders: replace broken border-current/20
  (Tailwind can't apply opacity to currentColor) with per-tag border
  colour classes via new get_tag_border_css filter
- Add calendar icon before article date in article header
- Add clock icon before read time in article header and home featured
- Match article card footer to wireframe (remove extra min-read span)
- Add rounded-md to code block matching wireframe

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

templates/blog/home_page.html

@@ -34,7 +34,7 @@
         {% for tag in featured_article.tags.all %}
           <span class="text-xs font-mono font-bold px-2 py-1 {{ tag|get_tag_css }}">{{ tag.name }}</span>
         {% endfor %}
-        <span class="text-sm font-mono text-zinc-500">{{ featured_article.read_time_mins }} min read</span>
+        <span class="text-sm font-mono text-zinc-500"><svg class="w-3 h-3 inline mr-1 -mt-0.5" xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24" stroke-width="1.5" stroke="currentColor"><path stroke-linecap="round" stroke-linejoin="round" d="M12 6v6h4.5m4.5 0a9 9 0 1 1-18 0 9 9 0 0 1 18 0Z" /></svg>{{ featured_article.read_time_mins }} min read</span>
       </div>
       <a href="{{ featured_article.url }}">
         <h2 class="font-display font-black text-3xl md:text-5xl mb-4 group-hover:text-brand-cyan transition-colors leading-[1.1]">{{ featured_article.title }}</h2>