refactor(ocr): use stream .toList() instead of FQCN Collectors.toList()

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/main/java/org/raddatz/familienarchiv/service/OcrTrainingService.java

@@ -206,7 +206,7 @@ public class OcrTrainingService {
                 .map(OcrTrainingRun::getPersonId)
                 .filter(Objects::nonNull)
                 .distinct()
-                .collect(java.util.stream.Collectors.toList());
+                .toList();
         Map<String, String> personNames = new HashMap<>();
         if (!distinctPersonIds.isEmpty()) {
             personService.getAllById(distinctPersonIds)