refactor(A2): replace blender-renderer HTTP service with render-worker Celery container

- Create render-worker/ with Dockerfile (Ubuntu + cadquery + Blender via host mount)
- Add render-worker/check_version.py: verifies Blender >= 5.0.1 at startup, Exit 1 on failure
- Add render-worker/scripts/: blender_render.py, still_render.py, turntable_render.py
- Create backend/app/services/render_blender.py: direct subprocess rendering
  - convert_step_to_stl() and export_per_part_stls() using cadquery
  - render_still(): STEP → STL → PNG via Blender subprocess
  - is_blender_available(): detects BLENDER_BIN env for render-worker context
- Create backend/app/domains/rendering/tasks.py: render_still_task + render_turntable_task
- Update step_processor.py: use subprocess path when BLENDER_BIN env is set (render-worker)
- Update step_tasks.py: generate_stl_cache uses direct cadquery instead of HTTP
- Remove blender-renderer and threejs-renderer from docker-compose.yml
- Replace worker-thumbnail with render-worker (Ubuntu + cadquery + Blender mount)
- Remove Docker SDK from backend Dockerfile (was only for flamenco scaling)
- Update .env.example: BLENDER_VERSION=5.0.1 documented
- Update celery_app.py: include domains.rendering.tasks in autodiscover

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

docker-compose.yml

@@ -49,7 +49,6 @@ services:
     volumes:
       - ./backend:/app
       - uploads:/app/uploads
-      - /var/run/docker.sock:/var/run/docker.sock
     ports:
       - "8888:8888"
     depends_on:
@@ -86,11 +85,12 @@ services:
       redis:
         condition: service_healthy
 
-  worker-thumbnail:
+  render-worker:
     build:
-      context: ./backend
+      context: ./render-worker
       dockerfile: Dockerfile
-    command: celery -A app.tasks.celery_app worker --loglevel=info -Q thumbnail_rendering --concurrency=1
+      args:
+        - BLENDER_VERSION=${BLENDER_VERSION:-5.0.1}
     environment:
       - POSTGRES_DB=${POSTGRES_DB:-schaeffler}
       - POSTGRES_USER=${POSTGRES_USER:-schaeffler}
@@ -99,19 +99,25 @@ services:
       - POSTGRES_PORT=5432
       - REDIS_URL=${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
+      - BLENDER_BIN=/opt/blender/blender
+      - RENDER_SCRIPTS_DIR=/render-scripts
     volumes:
       - ./backend:/app
       - uploads:/app/uploads
+      - /opt/blender:/opt/blender:ro
     depends_on:
       postgres:
         condition: service_healthy
       redis:
         condition: service_healthy
+    deploy:
+      resources:
+        reservations:
+          devices:
+            - driver: nvidia
+              count: 1
+              capabilities: [gpu, compute, utility, graphics]
 
   beat:
     build:
@@ -140,36 +146,6 @@ services:
       redis:
         condition: service_healthy
 
-  blender-renderer:
-    build:
-      context: ./blender-renderer
-      dockerfile: Dockerfile
-    ports:
-      - "8100:8100"
-    volumes:
-      - uploads:/app/uploads
-      - ./blender-renderer:/app
-      - /opt/blender:/opt/blender:ro
-    restart: unless-stopped
-    deploy:
-      resources:
-        reservations:
-          devices:
-            - driver: nvidia
-              count: 1
-              capabilities: [gpu, compute, utility, graphics]
-
-  threejs-renderer:
-    build:
-      context: ./threejs-renderer
-      dockerfile: Dockerfile
-    ports:
-      - "8101:8101"
-    volumes:
-      - uploads:/app/uploads
-      - ./threejs-renderer:/app
-    restart: unless-stopped
-
   frontend:
     build:
       context: ./frontend