feat(reconcile): Phase 14D.1 cold-start handling

- Add detectColdStart() to check ledger state before drift/dashboard steps
- Skip drift/dashboard gracefully on cold-start (no ledger or < 2 runs)
- Return WARN verdict (exit 0) instead of FAIL for cold-start conditions
- Add ColdStartInfo interface and COLD_START_WARNINGS constants
- Add skipped flag to ReconcileStepResult for skipped steps
- Update computeOverall to treat skipped steps as WARN even in strict mode
- Add 8 cold-start tests (165 total reconcile tests pass)
- Document cold-start behavior in README CI Integration section

Fixes GitHub Actions FAIL on fresh checkout with no run ledger.