Collapse the four PCK and three OKS implementations into a single source of
truth — pck_canonical (torso hip↔hip, COCO/ADR-152 convention validated at
~96% PCK@20 in benchmarks/wiflow-std) and oks_canonical (scale from GT pose
extent). MetricsAccumulator, compute_pck/_per_joint/_oks, aggregate_metrics and
the deprecated *_v2 path all route through them, so Trainer::evaluate() and the
bench definition agree.
Fixes two claim-inflating bugs, each pinned by a regression test:
- zero-visible-joint PCK was 1.0 (false-perfect) -> now 0.0
- OKS s=1.0 on normalized coords made OKS~=1.0 for any pose ("fake Gold tier")
-> scale now derived from the pose; a 3x-torso-wrong pose yields OKS<0.2
Divergent local kernels (training_bench raw-threshold, sensing-server
torso-height) annotated "DO NOT USE for reported metrics". Legitimately changed
test expectations (all-coincident "perfect" fixtures are correctly unscoreable;
all-invisible -> 0.0) updated with comments citing the finding.
Co-Authored-By: claude-flow <ruv@ruv.net>
50b657459f