Replace the per-scene one-point getMotionBlur call (~5-6 ms/scene, B0-attributed
to IntersceneLma prepareLMA scaffolding + two ~THREADS_MAX thread-array spawns)
with OpticalFlow.getMotionBlurPoint: the identical double chain (setupERS x2,
getInterRotDeriveMatrices, getDPxSceneDParameters, same-order rate dot product)
run serially at the representative point - bit-for-bit the same result at ~us
cost. uniformMotionBlur broadcasts it unchanged; degenerate return still falls
back to legacy getMotionBlur (per-tile), so non-uniform behavior is untouched.

One-shot oracle at pose_lma_debug>=1 (replaces the closed B0 MB warm-repeat):
times the fast path, evaluates legacy getMotionBlur at the SAME representative
point, prints max|d| (expected 0 exactly). IntersceneLma.INFINITY_DISPARITY
becomes the single source for the 0.01 infinity threshold.

Gate (design doc B2): oracle max|d| = 0, real-scene poses within the B1 bounds,
MB setup ~6 -> <0.5 ms/scene. Needs Andrey's run to close.
Co-authored-by: Claude <claude@elphel.com>
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>