Add Vorlagen editor, upload portal, onboarding, and participant import command

- Dokument-Vorlagen-Editor: create/edit/reset document templates (admin)
- Upload-Portal: public portal for Nachweis uploads via token
- Onboarding: invite Destinatäre via email with multi-step wizard
- Bestätigungsschreiben: preview and send confirmation letters
- Email settings: SMTP configuration UI
- Management command: import_veranstaltung_teilnehmer for bulk participant import

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

compose.dev.yml

@@ -40,6 +40,7 @@ services:
       - LANGUAGE_CODE=de
       - TIME_ZONE=Europe/Berlin
       - REDIS_URL=redis://redis:6379/0
+      - CELERY_REDIS_URL=redis://redis:6379/2
       - PAPERLESS_API_URL=http://paperless:8000
       - PAPERLESS_API_TOKEN=1972509e25810d9ae7497c1c79ecfea9e942f18d
       - PAPERLESS_REQUIRED_TAG=Stiftung_Destinatäre
@@ -57,6 +58,44 @@ services:
       - ./app:/app
     command: ["python", "manage.py", "runserver", "0.0.0.0:8000"]
 
+  worker:
+    build: ./app
+    depends_on:
+      db:
+        condition: service_healthy
+      redis:
+        condition: service_started
+    environment:
+      - POSTGRES_DB=stiftung_dev
+      - POSTGRES_USER=postgres
+      - POSTGRES_PASSWORD=postgres_dev
+      - DB_HOST=db
+      - DB_PORT=5432
+      - DJANGO_SECRET_KEY=dev-secret-key-not-for-production
+      - DJANGO_DEBUG=1
+      - CELERY_REDIS_URL=redis://redis:6379/2
+    volumes:
+      - ./app:/app
+    command: ["celery", "-A", "core", "worker", "-l", "info"]
+
+  beat:
+    build: ./app
+    depends_on:
+      - redis
+      - db
+    environment:
+      - POSTGRES_DB=stiftung_dev
+      - POSTGRES_USER=postgres
+      - POSTGRES_PASSWORD=postgres_dev
+      - DB_HOST=db
+      - DB_PORT=5432
+      - DJANGO_SECRET_KEY=dev-secret-key-not-for-production
+      - DJANGO_DEBUG=1
+      - CELERY_REDIS_URL=redis://redis:6379/2
+    volumes:
+      - ./app:/app
+    command: ["celery", "-A", "core", "beat", "-l", "info"]
+
   paperless:
     image: ghcr.io/paperless-ngx/paperless-ngx:latest
     ports: