Migrate background tasks from FastAPI BackgroundTasks to Celery with Redis
for persistent task queuing, retries, and scheduled jobs.
Key changes:
- Add Celery configuration with Redis broker/backend
- Create task dispatcher with USE_CELERY feature flag for gradual rollout
- Add Celery task wrappers for all background operations:
- Marketplace imports
- Letzshop historical imports
- Product exports
- Code quality scans
- Test runs
- Subscription scheduled tasks (via Celery Beat)
- Add celery_task_id column to job tables for Flower integration
- Add Flower dashboard link to admin background tasks page
- Update docker-compose.yml with worker, beat, and flower services
- Add Makefile targets: celery-worker, celery-beat, celery-dev, flower
When USE_CELERY=false (default), system falls back to FastAPI BackgroundTasks
for development without Redis dependency.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
