FreeMoCap runtime adapter reads real 3D output into ADR-0005 frames

[rupertgermann]

Parent

• PRD: Real freemocap sidecar service #68

What to build

Add the real FreeMoCap-backed frame source behind the sidecar's internal source boundary. The sidecar should be able to use FreeMoCap camera/runtime output and convert it into the existing ADR-0005 sidecar-3d frame stream: 33 BlazePose landmarks, world-mm-3d coordinates, confidence, frame timestamps, and quality metadata. Keep FreeMoCap-specific behavior isolated so the HTTP/WebSocket contract and Rowing Tracker app-side client remain stable.

Acceptance criteria

• The sidecar can select a FreeMoCap-backed source instead of the synthetic source.
• FreeMoCap output is converted into schema-v2 sidecar-3d frames with 33 ordered keypoints and [x_mm, y_mm, z_mm, confidence] values.
• Frames include wall-clock timestamps suitable for the existing Rowing Tracker capture and alignment path.
• Reprojection/camera quality data is mapped into the existing frame quality fields where available.
• Malformed or incomplete FreeMoCap output is rejected with a clear sidecar error rather than streamed to the app.
• Tests cover adapter conversion using fixture or recorded FreeMoCap-like data without requiring hardware in CI.

Blocked by

• Installable sidecar CLI with contract-compatible synthetic source #69