feat: Create new model family for Claude 4.5

What does this merge request do and why?

• This will allow us to use new, trimmed down prompts
• See !3747 (closed)

How to set up and validate locally

1. Set up Agent Chat locally
2. Select Sonnet 4.5 model
3. Confirm that the 4.5-specific model is selected

Merge request checklist

• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.
• If this change requires executor implementation: verified that issues/MRs exist for both Go executor and Node executor or confirmed that changes are backward-compatible and don't break existing executor functionality.