feat: add page shell, preferences and translations

Base layout with top bar, role-based menu, profile menu and phone layout; theme, language and German form of address kept in cookies; German formal, German informal and English text; Fluent avatar bundled in the image by a Node build stage; placeholder pages for the Publisher and Admin groups.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N3t4WL7bd9bdHHNjEsxzqC

portal/shell/urls.py

@@ -0,0 +1,12 @@
+from django.urls import path
+
+from . import views
+
+urlpatterns = [
+    path("preferences", views.set_preferences, name="preferences"),
+    path("publish/announcements", views.publish_announcements, name="publish-announcements"),
+    path("administration/appearance", views.admin_appearance, name="admin-appearance"),
+    path("administration/settings", views.admin_settings, name="admin-settings"),
+    path("administration/audit", views.admin_audit, name="admin-audit"),
+    path("administration/status", views.admin_status, name="admin-status"),
+]