Summary

This PR adds Scene Viewer XR (SVXR)-style world-space AR placement, scale toggle functionality, and Y-axis movement capability to model-viewer, improving the XR experience to match industry standards.

Changes

• Initial Placement: Implemented optimal model placement logic for world-space AR that positions models at comfortable viewing distance and angle
• Scale Limits: Added min/max scale calculation to prevent models from becoming too small or large
• Scale Toggle: Added 1:1 scale toggle functionality that switches between initial scale and original model size
• Y-Axis Movement: Enhanced model positioning to allow full Y-axis control after initial placement

Technical Details

• Uses SVXR constants and algorithms for consistent behavior
• Adds proper scale clamping to prevent extreme sizes
• Enables Y-axis movement for more flexible model positioning
• Maintains backward compatibility with existing screen-space AR

Testing

Tested on Meta Quest 3

• Tested world-space AR initial placement with various model sizes
• Verified scale toggle functionality works correctly
• Confirmed scale limits prevent models from becoming too small or large
• Validated smooth transitions between scales
• Tested Y-axis movement for flexible model positioning