Improve “Branch in New Chat” Context Handling

Thanks for sharing this idea, @aliexe. I can definitely see why that would be useful, especially for long technical conversations where you want a branch to become a more focused discussion instead of carrying along unrelated history. Giving users control over how much context is copied, whether that's the full conversation, up to a selected message, AI-generated minimal context, or just the selected message, seems like a thoughtful way to make branching more flexible. I've passed this along to the team so it can be logged as a feature request. It's a great suggestion, and I appreciate you taking the time to explain both the current limitations and the potential improvements. -Mark G.