Datasette-llm 0.1a9 插件更新，Datasette Agent 无需显式配置默认模型

I have some big upgrades to Datasette Agent in the pipeline, but in the meantime here's a tiny user experience improvement to the underlying datasette-llm plugin.

It now picks up the default model used by LLM, which means you can start using Datasette Agent without needing to explicitly configure a default model:

uvx --with datasette-agent datasette content.db --internal internal.db

Previously you would also need to specify a model with -s plugins.datasette-agent.default_model gpt-6-astra.