✨ feat(config): override config bools with env vars

[welpo]

Summary

This PR introduces the ability to override boolean configuration flags through environment variables. Example, with sumi.toml containing quiet = true, you can do:

GIT_SUMI_QUIET=false git sumi '👷 misc(CI): rename git-sumi job'

And quiet will be correctly set to false:

💬 Input: "👷 misc(CI): rename git-sumi job"
✅ All 10 checks passed.

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How has this been tested?

• [X] Manual tests
• [ ] Unit tests
• [X] Integration tests

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Type of change

• [ ] Bug fix (fixes an issue without altering functionality)
• [X] New feature (adds non-breaking functionality)
• [ ] Breaking change (alters existing functionality)
• [ ] UI/UX improvement (enhances user interface without altering functionality)
• [ ] Refactor (improves code quality without altering functionality)
• [ ] Documentation update
• [ ] Other (please describe below)

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Checklist

• [X] I have read the contributing guidelines.
• [X] I have added tests to cover my changes.
• [X] All new and existing tests passed.
• [X] My code follows the code style of this project.
• [X] I have formatted the code with cargo fmt.
• [ ] My change requires updating the documentation.
• [ ] I have updated the documentation accordingly.