Bisection loop / orchestrator

The core bit that drives git bisect and coordinates everything else.

Needs to:
- Manage good/bad/skip state
- Call out to build and test steps each iteration
- Persist state so you can resume if something falls over
- Eventually support parallel (n-bisect) as well as sequential

Things to look at:
- kci-dev bisect (Denys) — client-side, sequential, JSON state
- Mark's k8s wrapper — parallel builds
- Guillaume's Renelec — API-driven

Open questions:
- Client-side, server-side, or both?
- Merge commits and non-linear history?
- What state actually needs saving?

Start by comparing the referenced kci-dev bisect client, Mark's Kubernetes wrapper, and Guillaume's Renelec implementation. Resolve the client/server boundary, history handling, saved state, and sequential versus parallel execution; done means the orchestrator's scope and requirements are agreed for implementation.

Written by the indexing model from the issue text.