fix(node): apply per-model arm type to gravity compensation

[JafarAbdi]

Pass arm_type to direct_scaling_factors and GravityCompensationModel so non-base arms get the correct per-model torque scaling in the node gravity comp.

Depends on Reimagine-Robotics/piper_control#86

[greptile-apps]

Greptile Summary

This PR applies the configured arm type to node gravity compensation. The main changes are:

• Resolve the configured arm type before gravity model creation.
• Pass the arm type to direct scaling-factor selection.
• Pass the arm type to the MuJoCo gravity model.

Confidence Score: 5/5

The changed gravity-compensation API boundary needs confirmation before merging.

• The node resolves the same configured arm type used for the robot interface.
• The external gravity-compensation API must accept that enum representation for all configured arm types.

src/piper_control_ros2/piper_control_ros2/piper_control_node.py

Important Files Changed

Filename	Overview
src/piper_control_ros2/piper_control_ros2/piper_control_node.py	Adds the configured arm type to gravity scaling and model construction.

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