docs(adr-150): calibration thesis is task-general (action recognition)

Verified on a 2nd MM-Fi task: 27-class action recognition (which MM-Fi
never benchmarked for WiFi; only published baseline WiDistill 34%). In-domain
88% (leaky); cross-subject zero-shot collapses to ~10%; few-shot calibration
rescues 10->76% (1000 samples). Same mechanism as pose -> few-shot in-room
calibration is the universal WiFi-sensing generalization answer, not a pose
quirk.

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