Move CrewAI pipeline to task queue (Celery/RQ)

[freesoft]

Phase 4: Server Architecture

CrewAI pipelines run in threading.Thread (web_tutor.py:857). Not scalable and subject to GIL.

Tasks

• Set up Celery or RQ with Redis broker
• Move generate_problem_bg, check_answer_bg, generate_scaffold_problem_bg to async tasks
• Keep SSE notification mechanism working with external workers

Files

• web_tutor.py