Fix #64: Obergrenze für .bak-Backup-Schleife

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

pdf-umbenenner-bootstrap/src/main/java/de/gecheckt/pdf/umbenenner/bootstrap/adapter/GuiConfigurationPropertiesWriter.java

@@ -117,7 +117,8 @@ public final class GuiConfigurationPropertiesWriter implements GuiConfigurationF
             LOG.info("Sicherungskopie erstellt: {}", bakPath);
             return;
         }
-        for (int i = 1; ; i++) {
+        final int MAX_BACKUP_ATTEMPTS = 1000;
+        for (int i = 1; i <= MAX_BACKUP_ATTEMPTS; i++) {
             Path numbered = targetPath.resolveSibling(targetPath.getFileName() + ".bak." + i);
             if (!Files.exists(numbered)) {
                 copyFile(targetPath, numbered);
@@ -125,6 +126,8 @@ public final class GuiConfigurationPropertiesWriter implements GuiConfigurationF
                 return;
             }
         }
+        throw new GuiConfigurationWriteException(
+                "Maximale Anzahl an .bak-Sicherungen (1000) für '" + targetPath + "' erreicht");
     }
 
     /**