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/config/settings.py

@@ -33,6 +33,7 @@ INSTALLED_APPS = [
     "django.contrib.staticfiles",
     "portal.audit",
     "portal.accounts",
+    "portal.shell",
 ]
 
 MIDDLEWARE = [
@@ -44,7 +45,7 @@ MIDDLEWARE = [
     "django.contrib.sessions.middleware.SessionMiddleware",
     "portal.accounts.middleware.AbsoluteSessionLimitMiddleware",
     "portal.accounts.middleware.CurrentUserMiddleware",
-    "django.middleware.locale.LocaleMiddleware",
+    "portal.shell.middleware.PreferencesMiddleware",
     "django.middleware.common.CommonMiddleware",
     "django.middleware.csrf.CsrfViewMiddleware",
     "django.middleware.clickjacking.XFrameOptionsMiddleware",
@@ -62,6 +63,7 @@ TEMPLATES = [
             "context_processors": [
                 "django.template.context_processors.request",
                 "django.template.context_processors.i18n",
+                "portal.shell.context.shell",
             ],
         },
     }