Installable sidecar CLI with contract-compatible synthetic source

[rupertgermann]

Parent

• PRD: Real freemocap sidecar service #68

What to build

Create the repo-owned Python sidecar package and console command so a developer can install and run rowing-tracker-sidecar locally without real cameras. The running service should satisfy the existing sidecar contract with a deterministic synthetic frame source, allowing Rowing Tracker to connect, start capture, receive schema-v2 sidecar-3d frames, stop capture, and finalize a session through the current app-side integration.

Acceptance criteria

• A repo-supported local install path provides a rowing-tracker-sidecar console command.
• Running the command on localhost exposes contract-compatible health, session start, session stop, and pose-stream endpoints.
• The synthetic source emits deterministic schema-v2 sidecar-3d frames with 33 keypoints and world-mm-3d coordinates.
• Rowing Tracker can connect to the synthetic sidecar from the existing Multi-camera sidecar UI and complete a capture/finalize flow.
• Automated tests cover CLI startup, health shape, one start/stop lifecycle, WebSocket frame shape, and app-side client compatibility without hardware.

Blocked by

None - can start immediately