fix: 重复提交配置改为幂等，返回已有记录而非报错

par-core/src/main/java/com/par/core/service/impl/ConfigServiceImpl.java

@@ -61,7 +61,8 @@ public class ConfigServiceImpl implements ConfigService {
                                    String schemaVersion, Long submitterId) {
         SiteConfig existing = getConfig(siteId, version);
         if (existing != null) {
-            throw new IllegalArgumentException("该版本已存在: " + version);
+            log.info("配置版本已存在，跳过: siteId={}, version={}", siteId, version);
+            return existing;
         }
 
         String configHash = HmacUtil.sha256(configJson);