Movie SBS converges on the screen plane, so real content sits at NEGATIVE
disparity; minDisparity=0 clipped everything behind convergence to black.
Window is now ±num_disp/2 with 2-98 percentile normalization and a validity
mask. Verified on Big Buck Bunny (half-OU) + One Night In Hell (half-SBS):
structured depth + colored clouds that render in Blender.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>