Sidecar: expand smoke/regression coverage for /health, /predict schema, and feedback

[sheawinkler]

Problem

• Sidecar regressions (stub mode, schema drift, missing fields) can slip through without failing fast.

Goal

• Strengthen automated checks so contract breaks are caught early.

Proposed changes

• Extend scripts/sidecar_smoke.sh to assert:
  • /health mode == expected, models_loaded > 0 in full mode
  • /predict response includes prediction, confidence, expected_return, score, latency_ms
  • metadata includes feature schema/version fields
• Add unit tests for request parsing + feature tensorization + feedback logging.

Acceptance criteria

• Smoke script exits non-zero on schema mismatch or missing required fields.
• pytest suite includes coverage for the critical parsing paths.