feat: add 0xA9 feedforward frame and wire feedforward controller to motor output

- host 0xA9 frame → master_machine decode → robot_cmd publish
  via gimbal_feedforward topic → gimbal subscribe → yaw_motor.feed_input
- add DM_Feedforward_Controller_s with Kp and feed_input fields
- add feedforward term (Kp * feed_input) to motor control output
- add DM_Feedforward_Kp to motor init config

application/robot_def.h

@@ -63,6 +63,12 @@ typedef struct
     float pitch_Kp, pitch_Ki, pitch_Kd;
 } Motor_PID_Tune_s;
 
+/* ---- CMD 发布给 gimbal 的前馈输入 ---- */
+typedef struct
+{
+    float feedforward;
+} Gimbal_Feedforward_s;
+
 #pragma pack()
 
 #endif // !ROBOT_DEF_H