KcpMobilityPawnsFeatures

Versioned, dice-independent 31-column feature contract (kcp-mobility-pawns-31-v1).

Keeps KcpMobilityFeatures.extract as an unchanged 27-column prefix, followed by passed-pawn counts (own_passed_pawns, opp_passed_pawns) and the rank of the most advanced passed pawn (own_passed_max_rank, opp_passed_max_rank), counted from that side's own back rank as 0 (so 1–6 for a pawn and 0 when none exists).

All features are evaluated from the explicit perspective of color, independent of active color and dice.