complete new audit system

frontend/src/pages/customers/CustomerForm.tsx

@@ -64,17 +64,17 @@ export default function CustomerForm() {
     // Only include the fields that can be updated - exclude relations and read-only fields
     const submitData: any = {
       type: data.type,
-      salutation: data.salutation || undefined,
+      salutation: data.salutation || '',
       firstName: data.firstName,
       lastName: data.lastName,
-      companyName: data.companyName || undefined,
-      email: data.email || undefined,
-      phone: data.phone || undefined,
-      mobile: data.mobile || undefined,
-      taxNumber: data.taxNumber || undefined,
-      commercialRegisterNumber: data.commercialRegisterNumber || undefined,
-      notes: data.notes || undefined,
-      birthPlace: data.birthPlace || undefined,
+      companyName: data.companyName || '',
+      email: data.email || '',
+      phone: data.phone || '',
+      mobile: data.mobile || '',
+      taxNumber: data.taxNumber || '',
+      commercialRegisterNumber: data.commercialRegisterNumber || '',
+      notes: data.notes || '',
+      birthPlace: data.birthPlace || '',
     };
 
     // Handle birthDate - convert non-empty string to ISO string, or null to clear