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]>

static/js/app.js

@@ -0,0 +1,14 @@
+// Small progressive enhancements. Everything works without JavaScript.
+document.addEventListener("click", async (event) => {
+  const button = event.target.closest("[data-copy]");
+  if (!button) return;
+  const input = document.querySelector(button.dataset.copy);
+  if (!input) return;
+  input.select();
+  try {
+    await navigator.clipboard.writeText(input.value);
+    button.textContent = "Kopiert ✓";
+  } catch {
+    button.textContent = "Bitte manuell kopieren";
+  }
+});