[Feature]: generate squash message

[azabujuban]

Description

On repositories that only allow squashed merges into the main branch, the history can quickly become hard to read—even when using the conventional commits standard. It would be very helpful if opencommit supported generating a single commit message for a squashed commit.

Suggested Solution

This could be implemented as a new CLI parameter that takes a commit range and produces one combined message. Another useful option would be to support interactive rebases, for example by hooking into prepare-commit-msg during squash operations.

Alternatives

Asking LLM to generate a message based on a list of commits.

Additional Context

No response