Fix total_tax field name in dashboard service

backend/src/modules/dashboard/dashboard.service.ts

@@ -36,10 +36,10 @@ export class DashboardService {
     // Calculate total tax (mock logic for now, should sum up tax fields)
     const invoices = await this.invoiceRepository.find({
       where: { tenant_id: tenantId, status: InvoiceStatus.APPROVED },
-      select: ['total_tax'],
+      select: ['tax_amount'],
     });
 
-    const totalTax = invoices.reduce((sum, inv) => sum + Number(inv.total_tax || 0), 0);
+    const totalTax = invoices.reduce((sum, inv) => sum + Number(inv.tax_amount || 0), 0);
 
     // Get recent activities (last 5 invoices)
     const recentInvoices = await this.invoiceRepository.find({