Add category taxonomy and navigation integration

Implements Issue #35 with category snippets, article category routing, category-aware templates, and category RSS feeds with tests.

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

templates/blog/home_page.html

@@ -140,6 +140,16 @@
     {% endif %}
 
     {% if available_tags %}
+    {% if available_categories %}
+    <div>
+      <h4 class="font-display font-bold mb-4 uppercase tracking-widest text-zinc-500 text-sm">Browse Categories</h4>
+      <div class="flex flex-wrap gap-2 mb-3">
+        {% for category in available_categories %}
+          <a href="/articles/category/{{ category.slug }}/" class="px-3 py-1.5 border border-zinc-200 dark:border-zinc-800 text-sm font-mono hover:border-brand-cyan hover:text-brand-cyan transition-colors">{{ category.name }}</a>
+        {% endfor %}
+      </div>
+    </div>
+    {% endif %}
     <div>
       <h4 class="font-display font-bold mb-4 uppercase tracking-widest text-zinc-500 text-sm">Explore Topics</h4>
       <div class="flex flex-wrap gap-2">