feature: Having LLM "proofread" user supplied commit message

[mikegehard]

Issue

Aider already has the ability to create an LLM generated commit message.

Once #2904 is added it will have the ability to combine that with a user generated commit message, hopefully outlining the "why" of the commit to capture some context for future reference.

I would like to add a new feature, disabled by default, that allows you to feed the full commit message into an LLM to help generate a better "why" message based on the diff.

The goal of this feature would be to help improve commit messages to better capture the "history" of the code.

This "history" could then be used as context for future developers to ask questions about the evolution of the codebase.

Version and model info

No response