Get the MLB plate-discipline profile for a player season

MLB-only route. Returns the single (player, season, role) plate-discipline document from plate_discipline — Swing%, O-Swing% (chase), Z-Swing%, SwStr%, Contact% / Z-Contact% / O-Contact%, and Zone%, plus the raw zone-conditional counters. Rates are raw fractions (0–1), null when the denominator is zero. role=batter reads the player’s discipline at the plate; role=pitcher reads the discipline he induces.