✨ 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?

• Manual tests
• Unit tests
• Integration tests

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Type of change

• Bug fix (fixes an issue without altering functionality)
• 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

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