feat: improve Wagtail admin editor experience for articles

- Add published_date field to ArticlePage with auto-populate from
  first_published_at on first publish, plus data migration backfill
- Surface go_live_at/expire_at scheduling fields in editor panels
- Reorganise ArticlePage editor with TabbedInterface (Content,
  Metadata, Publishing, SEO tabs)
- Add Articles PageListingViewSet to admin menu with custom columns
  (author, category, published date, status) and category/author filters
- Add Articles summary dashboard panel showing drafts, scheduled,
  and recently published articles
- Update all front-end queries and RSS feeds to use published_date
- Add 10 unit tests and 4 E2E tests for new admin features

Closes #39

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

apps/blog/wagtail_hooks.py

@@ -1,7 +1,17 @@
+from django.utils.html import format_html
+
+import django_filters
+from wagtail import hooks
+from wagtail.admin.filters import WagtailFilterSet
+from wagtail.admin.ui.components import Component
+from wagtail.admin.ui.tables import Column, DateColumn
+from wagtail.admin.ui.tables.pages import BulkActionsColumn, PageStatusColumn, PageTitleColumn
+from wagtail.admin.viewsets.pages import PageListingViewSet
 from wagtail.snippets.models import register_snippet
 from wagtail.snippets.views.snippets import SnippetViewSet
 
-from apps.blog.models import Category, TagMetadata
+from apps.authors.models import Author
+from apps.blog.models import ArticlePage, Category, TagMetadata
 
 
 class TagMetadataViewSet(SnippetViewSet):
@@ -22,3 +32,74 @@ class CategoryViewSet(SnippetViewSet):
 
 
 register_snippet(CategoryViewSet)
+
+
+# ── Articles page listing ────────────────────────────────────────────────────
+
+
+class ArticleFilterSet(WagtailFilterSet):
+    category = django_filters.ModelChoiceFilter(
+        queryset=Category.objects.all(),
+        empty_label="All categories",
+    )
+    author = django_filters.ModelChoiceFilter(
+        queryset=Author.objects.all(),
+        empty_label="All authors",
+    )
+
+    class Meta:
+        model = ArticlePage
+        fields = []
+
+
+class ArticlePageListingViewSet(PageListingViewSet):
+    model = ArticlePage
+    icon = "doc-full"
+    menu_label = "Articles"
+    menu_order = 200
+    add_to_admin_menu = True
+    name = "articles"
+    columns = [
+        BulkActionsColumn("bulk_actions"),
+        PageTitleColumn("title", classname="title"),
+        Column("author", label="Author", sort_key="author__name"),
+        Column("category", label="Category"),
+        DateColumn("published_date", label="Published", sort_key="published_date"),
+        PageStatusColumn("status", sort_key="live"),
+    ]
+    filterset_class = ArticleFilterSet
+
+
+@hooks.register("register_admin_viewset")
+def register_article_listing():
+    return ArticlePageListingViewSet("articles")
+
+
+# ── Dashboard panel ──────────────────────────────────────────────────────────
+
+
+class ArticlesSummaryPanel(Component):
+    name = "articles_summary"
+    template_name = "blog/panels/articles_summary.html"
+    order = 110
+
+    def get_context_data(self, parent_context):
+        context = super().get_context_data(parent_context)
+        context["drafts"] = (
+            ArticlePage.objects.not_live()
+            .order_by("-latest_revision_created_at")[:5]
+        )
+        context["scheduled"] = (
+            ArticlePage.objects.filter(go_live_at__isnull=False, live=False)
+            .order_by("go_live_at")[:5]
+        )
+        context["recent"] = (
+            ArticlePage.objects.live()
+            .order_by("-published_date")[:5]
+        )
+        return context
+
+
+@hooks.register("construct_homepage_panels")
+def add_articles_summary_panel(request, panels):
+    panels.append(ArticlesSummaryPanel())