feat: add e-mail change with confirmation and undo

Page at /email asks for the new address and the current password (shared failure counter with the password page, five requests per hour) and mails a one-hour confirmation link to the new address. Confirming writes the address and mails the old address a 24-hour undo link; undoing restores it, ends every session of the user and notifies the Admin (ADMIN_NOTIFY_EMAIL). Link pages show on GET and apply on POST; tokens are stored only as hashes, single use, and are blanked from every log line. New table owned by profile, German text, tests; review findings logged in the plan.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FocPJ75XPma7TcuYEMy8zm

portal/profile/migrations/0001_initial.py

@@ -0,0 +1,29 @@
+# Generated by Django 5.2.18 on 2026-10-19 07:52
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    initial = True
+
+    dependencies = [
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='PendingEmailChange',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('user_key', models.CharField(db_index=True, max_length=256)),
+                ('sam', models.CharField(max_length=256)),
+                ('kind', models.CharField(choices=[('confirm', 'Confirm'), ('undo', 'Undo')], max_length=10)),
+                ('token_hash', models.CharField(max_length=64, unique=True)),
+                ('old_address', models.CharField(blank=True, max_length=254)),
+                ('new_address', models.CharField(max_length=254)),
+                ('created_at', models.DateTimeField()),
+                ('expires_at', models.DateTimeField()),
+                ('used_at', models.DateTimeField(blank=True, null=True)),
+            ],
+        ),
+    ]