Fix OAuth according to HF official documentation

add

Add 'itsdangerous' dependency for session management and enhance OAuth configuration with scope validation and warnings for unsupported scopes in Hugging Face Spaces.

Update session management in FastAPI app, modify OAuth scopes in environment configuration, and enhance .env.example with session security details.

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.