Fix issue #67: Retry / regenerate doesn't take you to new response

[onitbot]

This pull request fixes #67.

The changes effectively address the reported issue through two key modifications:

1. Added an .onChange modifier in GeneratedView.swift that automatically updates the prompt's generationIndex whenever a new response is added to the responses array. This ensures that when a response is regenerated, the view will automatically show the newest response (prompt.generationIndex = prompt.responses.count - 1).

2. Added a test case (PromptGenerationTests.swift) that verifies this behavior by:

• Creating a test prompt with an initial response
• Adding a new response to simulate regeneration
• Verifying that the generationIndex updates to point to the new response

The core issue was that users had to manually navigate to new responses after regeneration. The implemented solution automatically updates the view to show the latest response by keeping the generationIndex synchronized with new responses. This is a straightforward fix that directly addresses the reported behavior without introducing complexity or potential side effects.

The changes are minimal but target the exact problem - the lack of automatic navigation to new responses - making it a focused and effective solution.

Automatic fix generated by OpenHands 🙌