refactor(A1): remove Flamenco, simplify render pipeline to Celery-only

- Remove flamenco-manager and flamenco-worker from docker-compose.yml
- Delete flamenco_client.py, flamenco_tasks.py, docker_scaler.py
- Simplify render_dispatcher.py to Celery-only (removes ~300 lines)
- Remove Flamenco beat schedule from celery_app.py
- Clean admin.py: remove flamenco settings, endpoints, threejs validation
- Clean orders.py cancel-render: Celery revoke only
- Clean worker.py: remove flamenco_job_id from activity response
- Migration 032: cancel lingering flamenco jobs, remove flamenco settings
- PLAN.md: mark all decisions confirmed, status IN UMSETZUNG

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

backend/app/tasks/celery_app.py

@@ -5,7 +5,7 @@ celery_app = Celery(
     "schaefflerautomat",
     broker=settings.redis_url,
     backend=settings.redis_url,
-    include=["app.tasks.step_tasks", "app.tasks.ai_tasks", "app.tasks.flamenco_tasks"],
+    include=["app.tasks.step_tasks", "app.tasks.ai_tasks"],
 )
 
 celery_app.conf.update(
@@ -17,20 +17,6 @@ celery_app.conf.update(
     task_routes={
         "app.tasks.step_tasks.*": {"queue": "step_processing"},
         "app.tasks.ai_tasks.*": {"queue": "ai_validation"},
-        "app.tasks.flamenco_tasks.*": {"queue": "step_processing"},
-    },
-    beat_schedule={
-        "poll-flamenco-jobs": {
-            "task": "app.tasks.flamenco_tasks.poll_flamenco_jobs",
-            "schedule": 10.0,  # every 10 seconds
-            # Discard if not consumed before the next run; prevents queue build-up
-            # when workers are busy with long-running STEP/render tasks.
-            "options": {"expires": 9},
-        },
-        "check-stalled-renders": {
-            "task": "app.tasks.flamenco_tasks.check_stalled_renders",
-            "schedule": 300.0,  # every 5 minutes
-            "options": {"expires": 290},
-        },
     },
+    beat_schedule={},
 )