perf: fix critical O(n²) bottleneck in mergeSalesAndAdsData

- The ads-only metadata lookup was doing a nested forEach (O(ads × sales))
- Now pre-builds asinMetadata map during sales aggregation for O(1) lookups
- This reduces complexity from O(n²) to O(n) for large datasets
- Should dramatically improve loading time for Weekly Sales tab

services/dataProcessor.ts

@@ -446,6 +446,9 @@ export const mergeSalesAndAdsData = (salesData: SalesRecord[], adsData: AdsRecor
     const createKey = (asin: string, customer: string, year: number, week: number) =>
         `${asin.trim().toUpperCase()}|${customer.trim().toUpperCase()}|${year}|${week}`;
 
+    // Pre-build metadata lookup map for O(1) access (instead of O(n) nested loop)
+    const asinMetadata = new Map<string, { sku: string; title: string; line: string }>();
+
     // 1. Aggregate Sales by ASIN|Customer|Year|Week (combine all SKUs)
     const salesMap = new Map<string, {
         sellOut: number;
@@ -462,15 +465,21 @@ export const mergeSalesAndAdsData = (salesData: SalesRecord[], adsData: AdsRecor
 
     salesData.forEach(sale => {
         const weekNum = sale.week || 0;
-        if (weekNum === 0) return; // Skip records without week data for weekly analysis
+        if (weekNum === 0) return;
 
         const key = createKey(sale.asin, sale.customer, sale.year, weekNum);
 
+        // Build metadata map: ASIN|Customer -> best metadata
+        const metaKey = `${sale.asin.trim().toUpperCase()}|${sale.customer.trim().toUpperCase()}`;
+        const existingMeta = asinMetadata.get(metaKey);
+        if (!existingMeta || (sale.title && sale.title.length > (existingMeta.title?.length || 0))) {
+            asinMetadata.set(metaKey, { sku: sale.sku, title: sale.title, line: sale.line });
+        }
+
         if (salesMap.has(key)) {
             const existing = salesMap.get(key)!;
             existing.sellOut += sale.sellOut;
             existing.units += sale.units;
-            // Keep the best metadata (longest title, first non-empty SKU)
             if (sale.title && sale.title.length > (existing.title?.length || 0)) {
                 existing.title = sale.title;
             }
@@ -513,7 +522,7 @@ export const mergeSalesAndAdsData = (salesData: SalesRecord[], adsData: AdsRecor
     const mergedData: CombinedKPIs[] = [];
     const processedKeys = new Set<string>();
 
-    // 3. Create ONE record per ASIN/Customer/Year/Week from sales, attach ads if available
+    // 3. Create ONE record per ASIN/Customer/Year/Week from sales
     salesMap.forEach((sale, key) => {
         processedKeys.add(key);
         const ad = adsMap.get(key);
@@ -529,7 +538,6 @@ export const mergeSalesAndAdsData = (salesData: SalesRecord[], adsData: AdsRecor
         const salesOrganic = Math.max(0, salesTotal - adSales);
         const unitsOrganic = Math.max(0, unitsTotal - adUnits);
 
-        // KPIs
         const acos = adSales > 0 ? (adCost / adSales) * 100 : 0;
         const tacos = salesTotal > 0 ? (adCost / salesTotal) * 100 : 0;
         const roas = adCost > 0 ? adSales / adCost : 0;
@@ -568,18 +576,11 @@ export const mergeSalesAndAdsData = (salesData: SalesRecord[], adsData: AdsRecor
         });
     });
 
-    // 4. Add ads-only records (ASINs with ads but no sales in the filtered data)
+    // 4. Add ads-only records - use O(1) metadata lookup instead of O(n) loop
     adsMap.forEach((ad, key) => {
         if (!processedKeys.has(key)) {
-            // Look up metadata from sales data for this ASIN (any week)
+            const metaKey = `${ad.asin.trim().toUpperCase()}|${ad.country.trim().toUpperCase()}`;
-            let meta: { sku: string; title: string; line: string } | undefined;
+            const meta = asinMetadata.get(metaKey);
-            salesMap.forEach((sale, saleKey) => {
-                if (saleKey.startsWith(ad.asin.trim().toUpperCase() + '|' + ad.country.trim().toUpperCase())) {
-                    if (!meta || sale.title?.length > meta.title?.length) {
-                        meta = { sku: sale.sku, title: sale.title, line: sale.line };
-                    }
-                }
-            });
 
             mergedData.push({
                 id: `ads-only-${key}`,