fix: correct ad spend over-calculation in Weekly Grid

- Refactored mergeSalesAndAdsData to aggregate by ASIN+Customer+Year+Week
- Each ASIN/Week now produces exactly one output record
- Updated pivotWeeklySalesData to use ASIN as primary key
- Fixed double-counting when same ASIN had multiple SKUs
- Added support for ads-only records (ASINs with spend but no sales)
- Changed App.tsx to use filtered ads data for accurate totals

App.tsx

@@ -248,8 +248,8 @@ const App: React.FC = () => {
 
   // Combine Sales & Ads Data dynamically based on current filters
   const combinedAdsData = useMemo(() => {
-    return mergeSalesAndAdsData(filteredData, adsData);
-  }, [filteredData, adsData]);
+    return mergeSalesAndAdsData(filteredData, filteredAdsData);
+  }, [filteredData, filteredAdsData]);
 
   // Derive Context Data (Product Line Context when drilling down)
   const contextAggregatedData = useMemo(() => {