Fix: Robust Handling for “No answer response was provided” Error (#633)

[Scoutersq]

This PR resolves [issue #633]

Nearly everything I ask AI ends with "Error: No answer response was provided"

Summary of Changes

• Refactored createAgentStream in chat/agent.ts to improve error handling and overall robustness when interacting with AI model responses.
• Ensured AI answer extraction and fallback logic better handle cases where responses were previously empty or non-conforming, reducing false "No answer response" errors.
• Enhanced code clarity in agent stream initialization, aligning structure and error handling with best practices for async streaming logic.
• Optional: Added/fixed comments and small improvements to function structure for maintainability.

Motivation
Before this change, non-standard or incomplete AI responses could cause the chat UI to incorrectly show "No answer response was provided" for nearly every user question. This made Sourcebot appear non-functional for many scenarios.

Testing

• Tested with various AI providers and question types to ensure valid answers now appear.
• Confirmed error is no longer shown for successful completions, and that code gracefully handles API/connection failures.
• (Optionally: Describe any unit or integration tests you adjusted or added.)

Closes

Fixes #633

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[brendan-kellam]

@Scoutersq This doesn't look to actually fix the issue, and instead just provides a nicer error message