refactor(online): 使用常量替换硬编码的元数据源字符串

common/common-online/src/main/java/apelet/common/online/controller/OnlinePageController.java

@@ -75,6 +75,10 @@ public class OnlinePageController {
     @Autowired
     private IOnlFormFieldService onlFormFieldService;
 
+    //new=新建元数据，exist=现有元数据
+    private static final String META_SOURCE_NEW = "new";
+    private static final String META_SOURCE_EXIST = "exist";
+
     /**
      * 新增在线表单页面数据。
      *
@@ -92,7 +96,7 @@ public class OnlinePageController {
         }
         // Validate based on metaSource
         String metaSource = onlinePageDto.getMetaSource();
-        if ("new".equals(metaSource)) {
+        if (META_SOURCE_NEW.equals(metaSource)) {
             // New metadata flow: metaType and pageCode are required
             if (StrUtil.isEmpty(onlinePageDto.getMetaType())) {
                 errorMessage = "数据验证失败，新建元数据时表类型(metaType)不能为空！";
@@ -117,7 +121,7 @@ public class OnlinePageController {
 
         OnlFormHead onlFormHead;
 
-        if ("new".equals(metaSource)) {
+        if (META_SOURCE_NEW.equals(metaSource)) {
             // === New branch: create fresh metadata ===
             String metaType = onlinePageDto.getMetaType();
             String tableName = onlinePageDto.getPageCode();