bpm-engine 0.2.0

Lightweight embeddable BPM runtime for long-running, stateful workflows with tokens, timers, Saga compensation, and crash recovery
Documentation
## Description

Brief description of the change.

## Type of change

- [ ] Bug fix
- [ ] New feature
- [ ] Documentation
- [ ] Refactor / cleanup
- [ ] Other (describe):

## Related issue(s)

Fixes # (if applicable).

## Checklist

- [ ] Code follows project style (`cargo fmt`, `cargo clippy`).
- [ ] Tests added or updated; `cargo test --workspace` passes.
- [ ] Documentation updated if needed (README, docs/, doc comments).
- [ ] Change fits project focus (correctness, execution semantics, persistence).