refactor(b1): tidy ForwardTracker imports + module docstring

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/fxhnt/application/forward_tracker.py

@@ -1,15 +1,17 @@
-"""Forward-validation tracker for the combined book — the only ground truth before capital.
+"""Strategy-agnostic forward-validation tracker — the only ground truth before capital.
 
-Freezes the strategy at INCEPTION (first run) and, on each subsequent run, books only the realized returns
-of days STRICTLY AFTER inception — a genuine out-of-sample-in-time paper track (no capital risked). Run
-daily on a cron alongside the data fetch; the forward NAV + forward Sharpe accumulate honestly. The
-in-sample backtest Sharpe (~1.4) means nothing until the forward record confirms it.
+`ForwardTracker` freezes any `ForwardStrategy` port at INCEPTION and thereafter books only realized
+returns of days STRICTLY AFTER it — a genuine out-of-sample-in-time paper track (no capital risked).
+The combined book is one (recomputable) strategy on it; in-sample backtest Sharpe means nothing until
+the forward record confirms it.
 """
 from __future__ import annotations
 
+import datetime as _dt
 import json
 import os
 from dataclasses import dataclass
+from typing import Any, Protocol
 
 import numpy as np
 
@@ -30,10 +32,6 @@ class ForwardStatus:
     booked_today: int
 
 
-import datetime as _dt
-from typing import Any, Protocol
-
-
 class ForwardStrategy(Protocol):
     def advance(self, last_date: str | None, extra: dict[str, Any]) -> tuple[list[tuple[str, float]], dict[str, Any]]:
         """Return candidate (ISO-date, fractional-return) rows the strategy knows now, plus its updated