Improve error handling and user-facing messages

[freesoft]

Phase 5: Frontend & Deployment

Most errors are generic send_event(session_id, "error_msg", ...).

Tasks

• Categorize errors (user error vs server error vs LLM error)
• Show user-friendly messages in the UI
• Add retry logic for transient LLM failures

Files

• web_tutor.py, templates/index.html