Replace AVP mechanical package

[zc-xzc]

Summary

• Replace the existing AVP mechanical package in robot_platform with the updated package from avp_model.
• Remove the old full-installation HTML-centric material and keep the streamlined STL/STEP-based package.
• Keep the BOM, printable parts, images, and mechanical install guide aligned with the latest source package.

Validation

• Synchronized the package contents from the source repository.
• Verified only the intended AVP mechanical package files changed.