Only stiffen waist_pitch, leave waist_roll at default

Stiffening both axes caused shakiness during walking. Only pitch
(forward/backward tilt) was the original problem. Roll left at
default Kp=28.5 to avoid fighting lateral balance during gait.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

gear_sonic_deploy/src/g1/g1_deploy_onnx_ref/src/g1_deploy_onnx_ref.cpp

@@ -2842,8 +2842,8 @@ class G1Deploy {
       // avoid stripping gears against a clamp, but without the clamp the waist
       // flops under dynamic loads. Higher gains keep it rigid.
       // MuJoCo 13 = waist_roll, 14 = waist_pitch.
-      motor_command_tmp.kp.at(13) = 125.0f;
-      motor_command_tmp.kd.at(13) = 7.0f;
+      // Only stiffen waist_pitch (14) — the backward tilt axis.
+      // Leave waist_roll (13) at default to avoid fighting lateral balance.
       motor_command_tmp.kp.at(14) = 125.0f;
       motor_command_tmp.kd.at(14) = 7.0f;
       // Optional pitch offset (keys 7/8). Default 0°.