fix: replace Math.max(...spread) with loop to prevent call stack overflow

Math.max(...largeArray) crashes when combinedAdsData has thousands of
records. Replaced with a simple for-loop to find the max year safely.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

components/BSRUnitsCorrelationChart.tsx

@@ -65,10 +65,13 @@ export const BSRUnitsCorrelationChart: React.FC<Props> = ({ bsrData, combinedSal
     ? activeMarket
     : (availableMarkets[0] ?? 'Amazon DE');
 
-  // Current year from sales data
+  // Current year from sales data — use reduce to avoid call stack overflow with large arrays
   const currentYear = useMemo(() => {
-    const years = combinedSalesData.map(r => r.year).filter(Boolean);
-    return years.length > 0 ? Math.max(...years) : new Date().getFullYear();
+    let max = 0;
+    for (const r of combinedSalesData) {
+      if (r.year && r.year > max) max = r.year;
+    }
+    return max > 0 ? max : new Date().getFullYear();
   }, [combinedSalesData]);
 
   // Per-market chart data: BSR avg + units sum aligned by week