Add phase 1: Docker setup, auth with invitations and roles

- Django 5.2 + PostgreSQL 17 via docker compose (app + db, volumes,
  healthcheck on /healthz, test profile running pytest against Postgres)
- Custom e-mail user model with user/admin roles
- Invitation-only registration with single-use, hashed, expiring links
- Admin area: invitations, role changes, deactivation, password reset
  via one-time link or temporary password (forced change on login)
- First admin created from ADMIN_EMAIL/ADMIN_PASSWORD on startup
- Login rate limiting per e-mail and IP (DB-backed, worker-safe)
- Proxy middleware honouring X-Forwarded-* only from TRUSTED_PROXIES,
  optional CLIENT_IP_HEADER (e.g. CF-Connecting-IP)
- Security headers (CSP, HSTS, Permissions-Policy), secure __Host- cookies
- Mobile-first German UI, CLAUDE.md, README, init-env script
- 65 tests for auth, permissions, proxy handling and rate limiting

Co-Authored-By: Claude Opus 5.5 <[email protected]>

templates/form_fields.html

@@ -0,0 +1,12 @@
+{% if form.non_field_errors %}
+<div class="msg msg-error" role="alert">{% for e in form.non_field_errors %}{{ e }}{% if not forloop.last %}<br>{% endif %}{% endfor %}</div>
+{% endif %}
+{% for field in form.visible_fields %}
+<div class="field{% if field.errors %} has-error{% endif %}">
+  <label for="{{ field.id_for_label }}">{{ field.label }}</label>
+  {{ field }}
+  {% if field.help_text %}<small class="help">{{ field.help_text }}</small>{% endif %}
+  {% for e in field.errors %}<small class="error">{{ e }}</small>{% endfor %}
+</div>
+{% endfor %}
+{% for field in form.hidden_fields %}{{ field }}{% endfor %}