fix: render pipeline + multi-tenancy bugs (B-Fix-1 through B-Fix-9)

- Remove worker-thumbnail (no Blender, was competing on thumbnail_rendering)
- Move render_order_line_task to thumbnail_rendering queue (render-worker)
- Restore template_service.py real implementation (fix circular import shim)
- Thread tenant_id through STEP upload, Excel import, product create
- Make system tables (output_types, materials, etc.) tenant_id nullable
- Fix tenants frontend 307-redirect: use trailing slash /tenants/
- Remove Flamenco + Three.js from Admin UI (unsupported)
- Set all output_types render_backend to celery (was flamenco)

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

docker-compose.yml

@@ -112,37 +112,6 @@ services:
       redis:
         condition: service_healthy
 
-  worker-thumbnail:
-    build:
-      context: ./backend
-      dockerfile: Dockerfile
-    command: celery -A app.tasks.celery_app worker --loglevel=info -Q thumbnail_rendering --concurrency=1
-    environment:
-      - POSTGRES_DB=${POSTGRES_DB:-schaeffler}
-      - POSTGRES_USER=${POSTGRES_USER:-schaeffler}
-      - POSTGRES_PASSWORD=${POSTGRES_PASSWORD:-schaeffler}
-      - POSTGRES_HOST=postgres
-      - POSTGRES_PORT=5432
-      - REDIS_URL=${REDIS_URL:-redis://redis:6379/0}
-      - JWT_SECRET_KEY=${JWT_SECRET_KEY:-changeme-in-production}
-      - AZURE_OPENAI_API_KEY=${AZURE_OPENAI_API_KEY:-}
-      - AZURE_OPENAI_ENDPOINT=${AZURE_OPENAI_ENDPOINT:-}
-      - AZURE_OPENAI_DEPLOYMENT=${AZURE_OPENAI_DEPLOYMENT:-gpt-4o}
-      - AZURE_OPENAI_API_VERSION=${AZURE_OPENAI_API_VERSION:-2024-02-01}
-      - UPLOAD_DIR=/app/uploads
-      - MINIO_URL=${MINIO_URL:-http://minio:9000}
-      - MINIO_USER=${MINIO_USER:-minioadmin}
-      - MINIO_PASSWORD=${MINIO_PASSWORD:-minioadmin}
-      - MINIO_BUCKET=${MINIO_BUCKET:-uploads}
-    volumes:
-      - ./backend:/app
-      - uploads:/app/uploads
-    depends_on:
-      postgres:
-        condition: service_healthy
-      redis:
-        condition: service_healthy
-
   render-worker:
     build:
       context: .