relayburn-cli library surface.
The CLI ships as a binary (burn) backed by src/main.rs. This
lib.rs exists so internal modules can be unit-tested with cargo test -p relayburn-cli and so future integration tests under tests/
can reach the harness substrate without re-declaring the module tree.
Today the only public surface here is [harnesses] — the HarnessAdapter
trait, the lazy registry, and the shared pending-stamp adapter factory
introduced in #248-b. Wave 2 PRs (claude / codex / opencode) will plug
their adapters in via [harnesses::registry]; the CLI binary will reach
them through lookup / list_harness_names.
Keeping this surface as a library crate alongside the binary lets the
Wave 2 fan-out PRs add per-adapter modules and unit tests without
disturbing main.rs.