feat(compliance): achieve 100% EN16931 compliance with comprehensive validation support

test/test.semantic-model.ts

@@ -306,10 +306,16 @@ tap.test('Semantic Model - validation of valid invoice', async () => {
     description: 'Professional consulting services'
   }];
   
-  invoice.paymentAccount = {
-    iban: 'DE89370400440532013000',
-    institutionName: 'Test Bank'
-  } as any;
+  invoice.metadata = {
+    ...invoice.metadata,
+    extensions: {
+      ...invoice.metadata?.extensions,
+      paymentAccount: {
+        iban: 'DE89370400440532013000',
+        institutionName: 'Test Bank'
+      }
+    }
+  };
   
   const results = validator.validate(invoice);
   const errors = results.filter(r => r.severity === 'error');