feat: add Novita AI as LLM provider

[Alex-wuhu]

Summary

Add Novita AI as a new LLM provider option in Crucix.

Changes

• add a raw-fetch Novita provider using Novita's OpenAI-compatible chat completions endpoint
• register novita in the LLM provider factory and config surface
• document the new provider and its default model in the README
• add focused unit tests for provider creation and request/response behavior

Configuration

LLM_PROVIDER=novita
LLM_API_KEY=your_novita_key
LLM_MODEL=moonshotai/kimi-k2.5

Endpoint: https://api.novita.ai/openai

Validation

• node --test test/llm-novita.test.mjs