Fix gripper encoder wrap correction

[branyang02]

What changed

• Extract the startup encoder-wrap adjustment into a testable helper.
• Restrict the adjustment to the six arm motors.
• Add a regression test proving a multi-turn seventh gripper motor is left unchanged.

Why

Linear grippers can legitimately travel beyond 2π radians. The existing startup loop applies its ±2π arm-encoder correction to every motor state, including the calibrated gripper. That changes the gripper motor offset while retaining the original calibration endpoints, putting feedback and commands in different coordinate frames.

This preserves the existing correction for arm joints while keeping calibrated gripper coordinates intact.

Validation

Not run yet at the operator's request because the robot is currently being used for another task. The regression test is included but has not been executed. No hardware, CAN interface, or robot process was accessed while preparing this change.