feat(ZUGFERD): Add dedicated ZUGFERD v1/v2 support and refine invoice format detection logic

ts/formats/cii/zugferd/zugferd.validator.ts

@@ -0,0 +1,18 @@
+import { CIIBaseValidator } from '../cii.validator.js';
+import { ValidationLevel } from '../../../interfaces/common.js';
+import type { ValidationResult } from '../../../interfaces/common.js';
+
+/**
+ * Validator for ZUGFeRD invoice format
+ */
+export class ZUGFeRDValidator extends CIIBaseValidator {
+  /**
+   * Validates ZUGFeRD XML against business rules
+   * @returns True if business validation passed
+   */
+  protected validateBusinessRules(): boolean {
+    // Implement ZUGFeRD-specific business rules
+    // For now, we'll just use the base CII validation
+    return true;
+  }
+}