zeph 0.21.2

Lightweight AI agent with hybrid inference, skills-first architecture, and multi-channel I/O
## Description

<!-- Brief description of your changes. -->

## Type of Change

- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
- [ ] Documentation update
- [ ] Refactoring (no functional changes)

## Related Issues

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## Checklist

- [ ] My code follows the project's code style guidelines
- [ ] I have run `cargo +nightly fmt --check` and fixed any issues
- [ ] I have run `cargo clippy --workspace -- -D warnings` and addressed all warnings
- [ ] I have added tests that prove my fix is effective or that my feature works
- [ ] All existing tests pass locally with my changes
- [ ] If env vars changed: `docker/` compose files updated and `scripts/check-env-vars.sh` passes