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/templates/accounts/home.html

@@ -1,11 +1,7 @@
 {% extends "accounts/base.html" %}
 {% load i18n %}
-{% block title %}{% trans "Welcome" %}{% endblock %}
+{% block title %}{% trans "Home" %}{% endblock %}
 {% block content %}
-<h1>{% blocktrans with name=portal_user.display_name %}Signed in as {{ name }}{% endblocktrans %}</h1>
-<p>{{ portal_user.user.sam }}</p>
-<form method="post" action="{% url 'logout' %}">
-  {% csrf_token %}
-  <button type="submit">{% trans "Sign out" %}</button>
-</form>
+<h1>{% blocktrans with name=portal_user.display_name %}Hello, {{ name }}{% endblocktrans %}</h1>
+<p class="lead">{% trans "You are signed in. More pages will follow here." %}</p>
 {% endblock %}