Security & HF Spaces fixes: Enable CSRF, auth middleware, persistent storage

add

Fix usage tracker to read user from session

dd

Fix session persistence and add detailed debugging

Fix middleware order and session access issues

Enhance authentication requirements for root and agentgraph endpoints

Enhance authentication middleware by adding HTTPException import

Implement mandatory authentication and usage tracking for OpenAI API protection

Fix HF Spaces authentication: support __sign parameter and make auth optional

Implement conditional authentication middleware and OAuth routes for Hugging Face Spaces integration. Enhance environment debugging and add environment info endpoint. Update README with OAuth configuration details and improve startup logging.