Adds `fxt-backtest verdict <sweep_dir> --threshold X --windows W1,W2,W3,W4
--training-sha SHA --spec-sha SHA --out deployability_verdict.json`
that reads per-cell summary.json files at the realistic (1 tick, 200ms)
+ stress (1.5 tick, 400ms) anchors against the pre-registered threshold,
computes median Sharpe/max_dd/Sortino/profit_factor across windows,
classifies into Pass-robust / Pass-nominal / Fail-inconclusive / Fail /
Fail-degenerate per spec §3.5, and writes the audit JSON.
Adds serde_json workspace dep to fxt-backtest's Cargo.toml (was already
a transitive dep but not declared at this layer).
End-to-end CLI for Phase 2 runtime is now: argo-train.sh → argo-lob-sweep.sh
(smoke / threshold-tuning / deployability) → fxt-backtest aggregate →
fxt-backtest verdict → commit deployability_verdict.json.
58b5ebbd38