feat: Implement Pan-EU grouping in Grid tab

- Added applyPanEUGrouping() helper function in dataProcessor.ts
- Groups Amazon DE/IT/FR/ES as 'Pan-EU' when no customer filter applied
- Shows individual countries when specific filter is selected
- Updated DataGrid to accept hasCustomerFilter prop
- Updated App.tsx to pass filter state to DataGrid
- Keeps Amazon UK and Amazon SC separate
- Verified with browser testing: grouping works correctly

components/DataGrid.tsx

@@ -3,11 +3,12 @@ import {
     LineChart, Line, XAxis, YAxis, CartesianGrid, Tooltip, Legend, ResponsiveContainer
 } from 'recharts';
 import { SalesRecord, PivotRow } from '../types';
-import { pivotSalesData, generateCSV, aggregateForTimeSeries, aggregateForComparisonTimeSeries } from '../services/dataProcessor';
+import { pivotSalesData, generateCSV, aggregateForTimeSeries, aggregateForComparisonTimeSeries, applyPanEUGrouping } from '../services/dataProcessor';
 import { DownloadIcon, FunnelIcon, CloseIcon, ChartIcon } from './Icons';
 
 interface DataGridProps {
     data: SalesRecord[];
+    hasCustomerFilter: boolean;
 }
 
 type SortConfig = {
@@ -224,7 +225,7 @@ const ExpandableChartCard: React.FC<{ title: string; children: React.ReactNode;
 };
 
 
-const DataGrid: React.FC<DataGridProps> = ({ data }) => {
+const DataGrid: React.FC<DataGridProps> = ({ data, hasCustomerFilter }) => {
     const [currentPage, setCurrentPage] = useState(1);
     const [sortConfig, setSortConfig] = useState<SortConfig>({ key: null, direction: 'desc' });
     const [showChart, setShowChart] = useState(true);
@@ -248,8 +249,11 @@ const DataGrid: React.FC<DataGridProps> = ({ data }) => {
 
     // Transform flat data into Pivot structure
     const { rows: pivotRows, years } = useMemo(() => {
-        return pivotSalesData(data, effectiveDimensions);
-    }, [data, effectiveDimensions]);
+        // Apply Pan-EU grouping when no customer filter is applied
+        const processedData = applyPanEUGrouping(data, hasCustomerFilter);
+
+        return pivotSalesData(processedData, effectiveDimensions);
+    }, [data, effectiveDimensions, hasCustomerFilter]);
 
     // Data for the time series chart, supporting single and multi-year comparison
     const { chartData, uniqueYears, isComparisonView, chartTitle } = useMemo(() => {