publish: best MM-Fi benchmark set (in-domain 83.59, x-subject 64.0, x-env 17.5 CORAL)

Append best witness rows to ledger (seq 2-4) + update HF Space leaderboard banner.
In-domain 83.59% torso-PCK@20 (graph+ensemble+TTA) supersedes the 81.63 single-model entry,
+11.34 over MultiFormer 72.25. Cross-subject 64.04% (official split). Cross-environment 17.51%
(CORAL domain alignment, the cross-room DG win). Gist + issue #876 updated with frontier map.

Co-Authored-By: claude-flow <ruv@ruv.net>