fix: Correct production deployment to use pre-built Docker images

CRITICAL: This fixes the deployment issue where changes weren't appearing on production

Changes:
- Update docker-compose.prod.yml to use ghcr.io pre-built images instead of local builds
- Fix deployment script to pull latest images rather than building locally
- Add proper GitHub Container Registry authentication
- Remove --build flag that was causing deployment to use stale local code

This should resolve the issue where www.vhtv-stiftung.de wasn't showing the new Verpachtung features.

deploy-production/docker-compose.prod.yml

@@ -36,9 +36,7 @@ services:
           cpus: '0.5'
 
   web:
-    build: 
-      context: ../app
-      dockerfile: Dockerfile
+    image: ghcr.io/remmerinio/stiftung-management-system:main
     restart: unless-stopped
     environment:
       - DEBUG=False
@@ -66,9 +64,7 @@ services:
       - "127.0.0.1:8000:8000"
 
   worker:
-    build: 
-      context: ../app
-      dockerfile: Dockerfile
+    image: ghcr.io/remmerinio/stiftung-management-system:main
     restart: unless-stopped
     command: celery -A core worker -l info --concurrency=2
     environment:
@@ -93,9 +89,7 @@ services:
           cpus: '0.5'
 
   beat:
-    build: 
-      context: ./app
-      dockerfile: Dockerfile
+    image: ghcr.io/remmerinio/stiftung-management-system:main
     restart: unless-stopped
     command: celery -A core beat -l info --scheduler django_celery_beat.schedulers:DatabaseScheduler
     environment: