feat: add Novita AI as optional LLM provider

[Alex-wuhu]

Summary

• add a pre-configured Novita provider file using OpenAI-compatible API settings
• include Novita provider config in Docker image under /opt/pentagi/conf
• document Novita ctester usage and environment setup in README
• add Novita-specific env hints in .env.example

Notes

• integration follows existing custom provider flow via LLM_SERVER_URL/LLM_SERVER_KEY/LLM_SERVER_CONFIG_PATH
• Novita endpoint used: https://api.novita.ai/openai

[asdek]

@Alex-wuhu thank you for the request, I'll change model list in the feature/next_release branch