Update app.py

feat: Integrate Plotly for enhanced point cloud visualizations and update requirements

fix: Update .gitattributes and .gitignore for .ply file handling

Add Example

fix: Update .gitignore and pair_metadata.json

fix: app.py

feat: Add pair metadata JSON and update build_pair_index script for file searching

fix: README

fix: Update Open3D version

feat: Add point cloud registration demo using Open3D and Gradio

initial commit