feat: replace hardcoded navigation with CMS-managed models

Replace static nav/footer links with Wagtail-managed NavigationMenuItem
and SocialMediaLink orderables on SiteSettings. Unpublished pages are
automatically excluded from rendering, fixing the dead-link problem.

- Extend SiteSettings with site_name, tagline, footer_description,
  copyright_text branding fields
- Add NavigationMenuItem orderable (link_page/link_url, show_in_header,
  show_in_footer, sort_order) with automatic live-page filtering
- Add SocialMediaLink orderable with platform icon templates
- New template tags: get_nav_items, get_social_links
- Update nav.html and footer.html to render from CMS data
- Data migration seeds existing hardcoded values for zero-change deploy
- Update seed_e2e_content command for test/dev environments
- 18 new tests covering models, template tags, and rendered output

Closes #32

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

apps/core/management/commands/seed_e2e_content.py

@@ -150,7 +150,10 @@ class Command(BaseCommand):
             ]
             if article_index_page:
                 nav_items.append(
-                    NavigationMenuItem(settings=settings, link_page=article_index_page, link_title="Articles", sort_order=1)
+                    NavigationMenuItem(
+                        settings=settings, link_page=article_index_page,
+                        link_title="Articles", sort_order=1,
+                    )
                 )
             if about_page:
                 nav_items.append(
@@ -161,8 +164,15 @@ class Command(BaseCommand):
         if not SocialMediaLink.objects.filter(settings=settings).exists():
             SocialMediaLink.objects.bulk_create(
                 [
-                    SocialMediaLink(settings=settings, platform="twitter", url="https://twitter.com/nohypeai", label="Twitter (X)", sort_order=0),
-                    SocialMediaLink(settings=settings, platform="rss", url="/feed/", label="RSS Feed", sort_order=1),
+                    SocialMediaLink(
+                        settings=settings, platform="twitter",
+                        url="https://twitter.com/nohypeai",
+                        label="Twitter (X)", sort_order=0,
+                    ),
+                    SocialMediaLink(
+                        settings=settings, platform="rss",
+                        url="/feed/", label="RSS Feed", sort_order=1,
+                    ),
                 ]
             )
 

apps/core/models.py

@@ -6,7 +6,6 @@ from wagtail.admin.panels import FieldPanel, InlinePanel, MultiFieldPanel
 from wagtail.contrib.settings.models import BaseSiteSetting, register_setting
 from wagtail.models import Orderable
 
-
 SOCIAL_ICON_CHOICES = [
     ("twitter", "Twitter / X"),
     ("github", "GitHub"),

apps/core/tests/test_navigation.py

@@ -1,7 +1,7 @@
 import pytest
 from wagtail.models import Site
 
-from apps.blog.models import AboutPage, ArticleIndexPage, HomePage
+from apps.blog.models import AboutPage, ArticleIndexPage
 from apps.core.models import NavigationMenuItem, SiteSettings, SocialMediaLink
 
 
@@ -133,7 +133,7 @@ class TestSocialMediaLink:
 
     def test_ordering(self, site_with_nav):
         links = list(site_with_nav.social_links.all().order_by("sort_order"))
-        assert [l.platform for l in links] == ["twitter", "rss"]
+        assert [link.platform for link in links] == ["twitter", "rss"]
 
 
 @pytest.mark.django_db