feat: add password change

Password page with the AD policy listed first, ordered service (throttle limit below the lockout threshold, verification, local hints, directory change, ended sessions, audit and confirmation mail in one transaction), plain-language errors, German text and tests.

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

portal/templates/profile/password_unknown.html

@@ -0,0 +1,10 @@
+{% extends "base.html" %}
+{% load i18n %}
+{% block title %}{% trans "Result unclear" %}{% endblock %}
+{% block content %}
+<h1>{% trans "Result unclear" %}</h1>
+<div class="notice" role="alert">
+  <p>{% trans "Your password may have been changed, but the portal could not finish. Try to sign in with the new password. If that does not work, contact the administrator." %}</p>
+</div>
+<p><a class="button" href="{% url 'home' %}">{% trans "Back to the start page" %}</a></p>
+{% endblock %}