"""Build a self-contained HTML viewer for a decoded raiden recording.
Reads:
/robot_data.npz — proprio timelines
/mp4/.mp4 — decoded camera videos (per pyzed decode_svo2.py)
/mp4/.timestamps.json — per-frame ns timestamps (from decode_svo2.py)
Writes:
/viewer.html — 2x2 video grid + synced proprio plots
/viewer_data.json — proprio arrays + per-cam frame timestamps
The HTML uses Plotly for the joint/gripper plots and native