scope PR to a single router (nadir-cascade-v3-verifier)

Per /evaluate output: the workflow expects exactly two prediction files
per PR (the router + its -robustness companion). Removing the
nadir-cheapest-strategy-E files from this PR; they will be submitted in
a separate follow-up PR.

This PR now contains only nadir-cascade-v3-verifier:
- router_inference/router/nadir_adapter.py
- router_inference/router/NADIR_NOTES.txt
- router_inference/predictions/nadir-cascade-v3-verifier.json (10,018)
- router_inference/predictions/nadir-cascade-v3-verifier-robustness.json (420)
- router_inference/config/nadir-cascade-v3-verifier.json
- config/pipeline_config/nadir.json

Author: doramirdor