Enhance App component with view management by adding Tabs for Dashboard and Table views. Update DataViewer to receive current view and handle export data accordingly. Refactor BUTable to improve form validation and handle vst values more robustly. Update admin routes to ensure vst is correctly processed.

client/src/components/admin/BUTable.js

@@ -72,7 +72,7 @@ class BUTable extends Component {
       formData: bu ? {
         bu: bu.bu,
         name: bu.name,
-        vst: bu.vst || '',
+        vst: bu.vst !== null && bu.vst !== undefined ? bu.vst.toString() : '',
       } : {
         bu: '',
         name: '',
@@ -102,13 +102,20 @@ class BUTable extends Component {
     });
   };
 
+  isFormValid = () => {
+    const { formData } = this.state;
+    return formData.bu.trim() !== '' && 
+           formData.name.trim() !== '' && 
+           formData.vst !== '';
+  };
+
   handleSave = async () => {
     const { editingBU, formData } = this.state;
     
     // Convert vst to number or null
     const payload = {
       ...formData,
-      vst: formData.vst ? parseFloat(formData.vst) : null,
+      vst: formData.vst !== '' ? parseFloat(formData.vst) : null,
     };
     
     try {
@@ -220,7 +227,7 @@ class BUTable extends Component {
                   <TableCell>{bu.bu}</TableCell>
                   <TableCell>{bu.name}</TableCell>
                   <TableCell align="right">
-                    {bu.vst ? `${bu.vst}%` : '-'}
+                    {bu.vst !== null && bu.vst !== undefined ? `${bu.vst}%` : '-'}
                   </TableCell>
                   <TableCell align="right">
                     <IconButton
@@ -287,7 +294,11 @@ class BUTable extends Component {
           </DialogContent>
           <DialogActions>
             <Button onClick={this.handleCloseDialog}>Abbrechen</Button>
-            <Button onClick={this.handleSave} variant="contained">
+            <Button 
+              onClick={this.handleSave} 
+              variant="contained"
+              disabled={!this.isFormValid()}
+            >
               Speichern
             </Button>
           </DialogActions>