Move in-memory state to Redis

[freesoft]

Phase 4: Server Architecture

sse_queues, current_problems, scaffold_states are Python dicts in server memory (web_tutor.py:151-155). Lost on restart, can't scale horizontally.

Tasks

• Move session state to Redis
• Implement Redis pub/sub for SSE event delivery
• Handle TTL and cleanup

Files

• web_tutor.py