feat: 展示分块索引同步重试状态

- 返回当前版本任务的真实尝试次数与重试原因，区分模型服务和索引写入失败

- 分离提示与按钮布局，保持操作位置稳定，补充分块状态回归测试

easyflow-ui-admin/app/src/locales/langs/en-US/documentCollection.json

@@ -282,6 +282,10 @@
   "discardChanges": "Discard changes",
   "chunkSourceFallback": "Switched to source editing",
   "chunkSyncPending": "Updating search index",
+  "chunkSyncEmbeddingRetry": "Retrying embedding service ({attempt}/{maxAttempts})",
+  "chunkSyncVectorRetry": "Retrying vector index ({attempt}/{maxAttempts})",
+  "chunkSyncKeywordRetry": "Retrying keyword index ({attempt}/{maxAttempts})",
+  "chunkSyncIndexRetry": "Retrying search index ({attempt}/{maxAttempts})",
   "chunkSyncSucceeded": "Search index updated",
   "chunkSyncFailed": "Index sync failed. Click to retry",
   "chunkSyncRetryFailed": "Failed to retry index sync",