feat(postingkeys): allow VAT account postings to skip VAT amount validation

ts/skr.postingkeys.ts

@@ -85,7 +85,9 @@ export function validatePostingKey(
   }
 
   // Validate VAT requirement
-  if (rule.requiresVAT && !vatAmount) {
+  // Skip VAT amount requirement if posting TO a VAT account (the line itself IS the VAT)
+  const isVATAccount = accountNumber === '1571' || accountNumber === '1771' || accountNumber === '1576';
+  if (rule.requiresVAT && !vatAmount && !isVATAccount) {
     errors.push(
       `Posting key ${postingKey} requires VAT amount, but none provided. ` +
       `Description: ${rule.description}`