fix(experiments): prevent NaN propagation and ACOS zero-value bug in experiment analysis

- Change ?? to || for salesAds/units/revenue in weekly aggregation to guard against NaN
- Add || 0 fallback to ads-only records in mergeSalesAndAdsData
- Fix parseCurrency to check isNaN on all EU-format return paths
- Handle ACOS edge case: cost > 0 with adRevenue = 0 now returns 100% instead of 0%
- Add diagnostic console logging to computeDiD for data flow tracing

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

services/dataProcessor.ts

@@ -69,7 +69,8 @@ const parseCurrency = (value: string): number => {
         // Likely EU decimal without thousands or with thousands implicitly handled
         // e.g. "263,83" -> "263.83"
         clean = clean.replace(',', '.');
-        return parseFloat(clean);
+        const num = parseFloat(clean);
+        return isNaN(num) ? 0 : num;
     }
     else if (clean.includes(',') && clean.includes('.')) {
         // Mixed: 1.234,56 -> EU
@@ -79,7 +80,8 @@ const parseCurrency = (value: string): number => {
             // 1,234.56 -> US
             clean = clean.replace(/,/g, '');
         }
-        return parseFloat(clean);
+        const num = parseFloat(clean);
+        return isNaN(num) ? 0 : num;
     }
 
     // Case B: Standard/US Format or Clean Number (e.g. "277179.09" or "1000")
@@ -832,12 +834,12 @@ export const mergeSalesAndAdsData = (
                 sku: meta?.sku || '',
                 salesTotal: 0,
                 unitsTotal: 0,
-                salesAds: ad.attributedSales30d,
-                unitsAds: ad.attributedUnits30d,
-                cost: ad.cost,
-                clicks: ad.clicks,
-                impressions: ad.impressions,
-                conversions: ad.conversions,
+                salesAds: ad.attributedSales30d || 0,
+                unitsAds: ad.attributedUnits30d || 0,
+                cost: ad.cost || 0,
+                clicks: ad.clicks || 0,
+                impressions: ad.impressions || 0,
+                conversions: ad.conversions || 0,
                 salesOrganic: 0,
                 unitsOrganic: 0,
                 paidSalesShare: 0,