Implement smart merge of synced data to preserve external updates

src/App.tsx

@@ -113,15 +113,40 @@ export default function App() {
           console.log('Fetching synced data from Supabase...');
           const syncedData = await getAllSyncedRows(session?.access_token);
           
+          const editableColumns = new Set([
+            COLUMNS.LONG_DE, COLUMNS.LONG_EN, 
+            COLUMNS.SHORT_DE, COLUMNS.SHORT_EN,
+            COLUMNS.DETAILS_DE, COLUMNS.DETAILS_EN,
+            COLUMNS.INNER_L, COLUMNS.INNER_W, COLUMNS.INNER_H,
+            COLUMNS.OUTER_L, COLUMNS.OUTER_W, COLUMNS.OUTER_H,
+            COLUMNS.UNITS_OUTER, COLUMNS.MOQ
+          ]);
+          
+          headers.forEach((h: any, i: number) => {
+            const hl = String(h || '').toLowerCase();
+            if (hl.includes('srp') || hl.includes('uvp') || hl.includes('40') || hl.includes('price')) {
+              editableColumns.add(i);
+            }
+          });
+
           const articleNoIdx = COLUMNS.ARTICLE_NO;
           const processedRows = rows.map(row => {
             const articleNo = String(row[articleNoIdx]);
             const synced = syncedData[articleNo];
-            const finalRow = synced ? synced.data : row;
             
-            if (synced && synced.status === 'pending') {
+            const finalRow = [...row];
+            if (synced) {
+              // Smart Merge: Only overlay fields we logically "own" via this app's editors
+              editableColumns.forEach(idx => {
+                if (synced.data[idx] !== undefined && synced.data[idx] !== null) {
+                   finalRow[idx] = synced.data[idx];
+                }
+              });
+
+              if (synced.status === 'pending') {
                 setRowStatuses(prev => ({ ...prev, [articleNo]: 'pending' }));
               }
+            }
             
             return finalRow.map((val: any, idx: number) => {
               if (val === undefined || val === null || val === '') return val;