Implement new Kreditor creation functionality in BankingKreditorSelector component. Add state management for new Kreditor details, validation, and error handling. Enhance transaction handling to support banking transactions without IBAN. Update UI to allow users to create new Kreditors directly from the selector, including ID generation and validation feedback.

client/src/services/KreditorService.js

@@ -155,8 +155,9 @@ class KreditorService {
     // IBAN is only required for non-banking accounts that are not manual assignments
     const isBanking = kreditorData.is_banking || false;
     const hasIban = kreditorData.iban && kreditorData.iban.trim() !== '';
+    const isManualAssignment = kreditorData.is_manual_assignment || false;
     
-    if (!isBanking && !hasIban) {
+    if (!isBanking && !hasIban && !isManualAssignment) {
       errors.push('IBAN ist erforderlich (außer für Banking-Konten oder manuelle Zuordnungen)');
     }