Address PR review feedback

- Gate e2e-admin superuser behind E2E_MODE env var (security)
- Add status and tag filters to ArticleFilterSet
- Set default_ordering to -published_date on listing viewset
- Add summary to ArticlePage.search_fields for search support
- Add 4 new tests for filters, ordering, and search fields

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

apps/core/management/commands/seed_e2e_content.py

@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+import os
+
 from django.contrib.auth import get_user_model
 from django.core.management.base import BaseCommand
 from taggit.models import Tag
@@ -200,8 +202,8 @@ class Command(BaseCommand):
             ]
         )
 
-        # Admin user for E2E admin tests
-        if not User.objects.filter(username="e2e-admin").exists():
+        # Admin user for E2E admin tests — only when E2E_MODE is set
+        if os.environ.get("E2E_MODE") and not User.objects.filter(username="e2e-admin").exists():
             User.objects.create_superuser(
                 username="e2e-admin",
                 email="e2e-admin@example.com",