physics: sync server turn rate and fix SPLINE speed handlers

- Add getServerTurnRate() accessor and turnRateOverride_ field so the
  keyboard turn speed respects SMSG_FORCE_TURN_RATE_CHANGE from server
- Convert rad/s → deg/s before applying to camera yaw logic
- Fix SMSG_SPLINE_SET_RUN_BACK/SWIM/FLIGHT/FLIGHT_BACK/SWIM_BACK/WALK/
  TURN_RATE handlers: all previously discarded the value; now update the
  corresponding serverXxxSpeed_ / serverTurnRate_ field when GUID matches
  playerGuid (camera controller syncs these every frame)

include/game/game_handler.hpp

@@ -1158,6 +1158,7 @@ public:
     float getServerFlightSpeed() const { return serverFlightSpeed_; }
     float getServerFlightBackSpeed() const { return serverFlightBackSpeed_; }
     float getServerRunBackSpeed() const { return serverRunBackSpeed_; }
+    float getServerTurnRate() const { return serverTurnRate_; }
     bool isPlayerRooted() const {
         return (movementInfo.flags & static_cast<uint32_t>(MovementFlags::ROOT)) != 0;
     }