fix: enforce chronological rebalance scores

src/quant_engine/portfolio_construction.py

@@ -83,6 +83,8 @@ def scores_to_weight_table(
     _validate_gross_exposure(gross_exposure)
     if not scores.index.is_unique:
         raise ValueError("scores must contain unique rebalance dates")
+    if not scores.index.is_monotonic_increasing:
+        raise ValueError("scores rebalance dates must be in chronological order")
     if not scores.columns.is_unique:
         raise ValueError("scores must contain unique asset labels")
     if not all(is_numeric_dtype(dtype) for dtype in scores.dtypes):