refactor(b2): tilt uses statistics.median for consistency

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

src/fxhnt/domain/strategies/equity_factor.py

@@ -70,7 +70,7 @@ def construction_weights(scores: list[float], construction: str, quantile: float
     if n == 0:
         return []
     if construction == "tilt":
-        med = sorted(scores)[n // 2]
+        med = median(scores)
         pos = [max(0.0, s - med) for s in scores]
         tot = sum(pos)
         return [p / tot for p in pos] if tot > 0 else [1.0 / n] * n