clapfig 0.21.1

Rich, layered configuration for Rust CLI apps
Documentation 
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## Summary

<!-- 1-3 sentences: what changed and why. -->

## Checklist

- [ ] Changelog `Unreleased` section updated (or chore/docs-only)
- [ ] Project umbrella check passes locally — `scripts/{check,pre-commit,rust-pre-commit,ci.sh}` or `cargo fmt --check && cargo clippy -- -D warnings && cargo test` (or `cargo nextest run`)
- [ ] Tests added or updated for behavior changes

## Notes for reviewers

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