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/middleware.py

@@ -0,0 +1,24 @@
+from django.utils import translation
+from django.utils.cache import patch_vary_headers
+
+from . import preferences
+
+
+class PreferencesMiddleware:
+    """Read the preference cookies and activate the language for this request (AD-15)."""
+
+    def __init__(self, get_response):
+        self.get_response = get_response
+
+    def __call__(self, request):
+        prefs = preferences.from_request(request)
+        request.preferences = prefs
+        request.LANGUAGE_CODE = prefs.language_code
+        translation.activate(prefs.language_code)
+        try:
+            response = self.get_response(request)
+        finally:
+            translation.deactivate()
+        response.headers.setdefault("Content-Language", prefs.language)
+        patch_vary_headers(response, ("Cookie", "Accept-Language"))
+        return response