keybr-tui 0.2.0

A terminal typing trainer inspired by keybr.com with adaptive learning
## Summary

<!-- One or two sentences describing what changed and why. -->

## Type of change

- [ ] Bug fix
- [ ] New feature
- [ ] Refactor (no behavior change)
- [ ] Documentation update
- [ ] Build / CI change

## Related issues

<!-- Link via "Closes #123" or "Refs #123". -->

## How was this tested?

<!-- Describe your test plan. If this adds new tests, note where they live (e.g. `src/metrics.rs` unit tests, `tests/` integration tests). -->

## Pre-merge checklist

- [ ] `cargo fmt --all -- --check` passes locally
- [ ] `cargo clippy --all-targets -- -D warnings` passes locally
- [ ] `cargo test` passes locally
- [ ] Updated CHANGELOG.md if user-facing
- [ ] Updated docs/ if architecture or behavior changed
- [ ] No new external dependencies added without justification

## Screenshots / asciinema (UI changes)

<!-- For visually observable behavior changes, attach a terminal recording (asciinema) or screenshot. -->