Real camera health and calibration readiness gate

[rupertgermann]

Parent

• PRD: Real freemocap sidecar service #68

What to build

Make the sidecar's health/readiness behavior reflect the real camera rig and calibration state. A user should see accurate ready/initializing/error status in Rowing Tracker before capture starts, including camera count, fps, schema version, and useful diagnostics when the rig cannot produce valid sidecar-3d frames. Starting capture should fail clearly when cameras or calibration are not ready.

Acceptance criteria

• Health reports ready, initializing, or error based on real source, camera, and calibration state.
• Health includes fps, camera count, and schema version fields compatible with the current app-side readiness check.
• Calibration traceability is surfaced as a sidecar-owned calibration id when available.
• Capture start refuses to arm when the sidecar cannot produce schema-v2 sidecar-3d frames.
• Rowing Tracker shows useful sidecar readiness/error messages without needing browser calibration.
• Tests cover ready, initializing, incompatible/missing calibration, missing camera, and incompatible schema cases.

Blocked by

• Installable sidecar CLI with contract-compatible synthetic source #69
• FreeMoCap runtime adapter reads real 3D output into ADR-0005 frames #70