Migrate register_impact from impact-reg-konfai (pip + one-time glibc/LibTorch
shim) to the vboussot/elastix_impact Docker image running a rigid 6-DOF
EulerTransform with MIND + TotalSegmentator static features and a Mattes-MI
secondary metric. Delete scripts/setup_impact_konfai.sh.
Vendor ImpactLoss (vboussot/ImpactLoss) into src/impact_loss.py and add
impact_loss as a per-case semantic scoring metric in the benchmark runner.
Update docs (AGENTS.md, REGISTRATION_BENCHMARK.md) to reflect the
all-rigid pipeline set and the new Docker-based IMPACT runtime.
