refactor(adapters): retrait de execution_mode (mensonge structurel)

test(public_api): Phase B3-final cleanup — ajuster TestApiStableDoc

feat(services): Phase B3-final commit 6 — supprimer les 3 modules purement legacy

feat(migration): Phase B3 (partielle) — exposer RunOrchestrator + deprecation

feat(audit): Phase 4 — suppressions franches (rupture v2.0)

feat(sprint-S8): cohérence finale — renames test dirs, /metrics endpoint, SBOM workflow