Recapture the grounded chat example screenshot for Part 4

[jongalloway]

Summary

Recapture images/chat-example.png from the current .NET 10 AI Chat Web App template.

The refreshed screenshot should demonstrate the end-to-end RAG behavior described in Part 4 using the documents in the current snapshot.

Screenshot requirements

• Run the current GenAiLab application through GenAiLab.AppHost.
• Ask a question grounded in either Example_GPS_Watch.pdf or Example_Emergency_Survival_Kit.pdf.
• Show the user's question, a useful grounded response, and visible document citations.
• Ensure the answer is based on the selected sample document rather than a generic response.
• Avoid including endpoints, credentials, or other sensitive information.
• Replace images/chat-example.png at its existing path.

Documentation update

Add the refreshed image to Step 5 in Part 04 - AI Web Chat Template/README.md and give it descriptive alt text.