Implement Pydantic AI Summarization Agent with Mistral-large

Create a Pydantic AI agent (e.g., `SummarizerAgent`) that takes raw article text as input and uses the `Mistral-large` model to generate an `ArticleSummary` object. Ensure the agent's output is strictly validated against your `ArticleSummary` Pydantic model. Include Python code for initializing the agent and a sample call. Focus on the agent's ability to produce valid, structured output.