feat(validation): Implement EN16931 compliance validation types and VAT categories

- Added validation types for EN16931 compliance in `validation.types.ts`, including interfaces for `ValidationResult`, `ValidationOptions`, and `ValidationReport`.
- Introduced `VATCategoriesValidator` in `vat-categories.validator.ts` to validate VAT categories according to EN16931 rules, including detailed checks for standard, zero-rated, exempt, reverse charge, intra-community, export, and out-of-scope services.
- Enhanced `IEInvoiceMetadata` interface in `en16931-metadata.ts` to include additional fields required for full standards compliance, such as delivery information, payment information, allowances, and charges.
- Implemented helper methods for VAT calculations and validation logic to ensure accurate compliance with EN16931 standards.

scripts/download-schematron.ts

@@ -0,0 +1,64 @@
+#!/usr/bin/env node
+
+/**
+ * Script to download official Schematron files for e-invoice validation
+ */
+
+import { SchematronDownloader } from '../ts/formats/validation/schematron.downloader.js';
+
+async function main() {
+  console.log('📥 Starting Schematron download...\n');
+  
+  const downloader = new SchematronDownloader('assets/schematron');
+  await downloader.initialize();
+  
+  // Download EN16931 Schematron files
+  console.log('🔵 Downloading EN16931 Schematron files...');
+  try {
+    const en16931Paths = await downloader.downloadStandard('EN16931');
+    console.log(`✅ Downloaded ${en16931Paths.length} EN16931 files`);
+    en16931Paths.forEach(p => console.log(`   - ${p}`));
+  } catch (error) {
+    console.error(`❌ Failed to download EN16931: ${error.message}`);
+  }
+  
+  console.log('\n🔵 Downloading PEPPOL Schematron files...');
+  try {
+    const peppolPaths = await downloader.downloadStandard('PEPPOL');
+    console.log(`✅ Downloaded ${peppolPaths.length} PEPPOL files`);
+    peppolPaths.forEach(p => console.log(`   - ${p}`));
+  } catch (error) {
+    console.error(`❌ Failed to download PEPPOL: ${error.message}`);
+  }
+  
+  console.log('\n🔵 Downloading XRechnung Schematron files...');
+  try {
+    const xrechnungPaths = await downloader.downloadStandard('XRECHNUNG');
+    console.log(`✅ Downloaded ${xrechnungPaths.length} XRechnung files`);
+    xrechnungPaths.forEach(p => console.log(`   - ${p}`));
+  } catch (error) {
+    console.error(`❌ Failed to download XRechnung: ${error.message}`);
+  }
+  
+  // List cached files
+  console.log('\n📂 Cached Schematron files:');
+  const cached = await downloader.getCachedFiles();
+  cached.forEach(file => {
+    if (file.metadata) {
+      console.log(`   - ${file.path}`);
+      console.log(`     Version: ${file.metadata.version}`);
+      console.log(`     Format: ${file.metadata.format}`);
+      console.log(`     Downloaded: ${file.metadata.downloadDate}`);
+    } else {
+      console.log(`   - ${file.path} (no metadata)`);
+    }
+  });
+  
+  console.log('\n✅ Schematron download complete!');
+}
+
+// Run the script
+main().catch(error => {
+  console.error('❌ Script failed:', error);
+  process.exit(1);
+});