Add BYOLLM support with LiteLLM integration

[recursiveAF]

Summary

• Replace anthropic dependency with litellm
• Add provider selection to noot init (anthropic, openai, gemini, groq, ollama)
• Add config.py module for reading model from pyproject.toml
• Flow.spawn() now reads model from project config by default
• Add --provider flag for non-interactive init
• Update templates and tests

Test plan

• uv run pytest tests/ passes (14 tests)
• uv run ruff check src/ tests/ passes
• uv run pyright src/ passes
• Manual test with Anthropic API key
• Manual test with OpenAI API key

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