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/locale/de_DU/LC_MESSAGES/django.po

@@ -0,0 +1,28 @@
+# German, informal address (du); only the differences, the rest falls back to de
+msgid ""
+msgstr ""
+"Project-Id-Version: self-service-portal\n"
+"Language: de_DU\n"
+"MIME-Version: 1.0\n"
+"Content-Type: text/plain; charset=UTF-8\n"
+"Content-Transfer-Encoding: 8bit\n"
+"Plural-Forms: nplurals=2; plural=(n != 1);\n"
+
+msgid "You do not have permission to open this page."
+msgstr "Dazu fehlt dir die Berechtigung."
+
+#, python-format
+msgid "Hello, %(name)s"
+msgstr "Hallo, %(name)s"
+
+msgid "You are signed in. More pages will follow here."
+msgstr "Du bist angemeldet. Weitere Seiten folgen hier."
+
+msgid "You cannot sign in to the portal with this account. If you think this is a mistake, contact your administrator."
+msgstr "Mit diesem Konto kannst du dich nicht am Portal anmelden. Wenn du glaubst, dass das ein Fehler ist, wende dich an die Administration."
+
+msgid "You have been signed out"
+msgstr "Du wurdest abgemeldet."
+
+msgid "This is not possible right now. Please try again later."
+msgstr "Das ist gerade nicht möglich. Bitte versuche es später erneut."