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>

config/urls.py

@@ -6,7 +6,7 @@ from django.views.generic import RedirectView
 from wagtail import urls as wagtail_urls
 from wagtail.contrib.sitemaps.views import sitemap
 
-from apps.blog.feeds import AllArticlesFeed, TagArticlesFeed
+from apps.blog.feeds import AllArticlesFeed, CategoryArticlesFeed, TagArticlesFeed
 from apps.core.views import consent_view, robots_txt
 
 urlpatterns = [
@@ -18,6 +18,7 @@ urlpatterns = [
     path("consent/", consent_view, name="consent"),
     path("robots.txt", robots_txt, name="robots_txt"),
     path("feed/", AllArticlesFeed(), name="rss_feed"),
+    path("feed/category/<slug:category_slug>/", CategoryArticlesFeed(), name="rss_feed_by_category"),
     path("feed/tag/<slug:tag_slug>/", TagArticlesFeed(), name="rss_feed_by_tag"),
     path("sitemap.xml", sitemap),
     path("admin/", RedirectView.as_view(url="/cms/", permanent=False)),