feat: add RViz multi-material compatibility tool

[Yang-Ci]

Summary

• Add Rebot_Arm_description/tools/rviz_urdf_compat.py for ROS 2 Jazzy RViz multi-material rendering compatibility
• Update both English and Chinese READMEs with tool usage instructions

Problem

ROS 2 Jazzy's RViz renderer can assign a link's first material to all visuals within that link. Links with multiple differently-colored meshes therefore lose their per-part colors when loaded directly.

Solution

The compatibility script:

• Moves extra visuals into zero-offset fixed child links so each mesh keeps its own material
• Preserves original mesh poses, materials, and collision definitions
• Lightens RS black materials for RViz/Ogre display without altering the source URDF or Web/MuJoCo colors
• Writes converted output to stdout; never modifies the source URDF

Documentation

Both READMEs now cover:

• Command-line preview usage
• Python ROS 2 launch integration with Command and ParameterValue
• MoveIt integration via SourceFileLoader
• Installation guidance for ROS packages

Testing

• Verified the script runs successfully on both RS/urdf/ReBot_Arm_RS.urdf and DM/urdf/ReBot_Arm_DM.urdf
• Confirmed RS black material color overrides are applied
• Confirmed DM URDF parses and only receives the multi-visual split