fix(annotation): 解决空标注结果的状态处理问题

- 在构建标注快照时增加空标注检查，避免空对象被处理
- 修改状态判断逻辑，当标注为空且当前状态为 NO_ANNOTATION 或 NOT_APPLICABLE 时保持原状态
- 移除冗余的 hasExistingAnnotation 变量检查
- 确保空标注情况下状态流转的正确性，防止误标为已标注状态

frontend/src/pages/DataAnnotation/Annotate/LabelStudioTextEditor.tsx

@@ -192,6 +192,7 @@ const stableStringify = (value: unknown) => {
 
 const buildAnnotationSnapshot = (annotation?: Record<string, unknown>) => {
   if (!annotation) return "";
+  if (isAnnotationResultEmpty(annotation)) return "";
   const cleaned: Record<string, unknown> = { ...annotation };
   delete cleaned.updated_at;
   delete cleaned.updatedAt;
@@ -717,11 +718,13 @@ export default function LabelStudioTextEditor() {
     const annotationRecord = annotation as Record<string, unknown>;
     const currentTask = tasks.find((item) => item.fileId === String(fileId));
     const currentStatus = currentTask?.annotationStatus;
-    const hasExistingAnnotation = !!currentTask?.hasAnnotation;
     let resolvedStatus: AnnotationResultStatus;
     if (isAnnotationResultEmpty(annotationRecord)) {
-      if (currentStatus === AnnotationResultStatus.ANNOTATED || (hasExistingAnnotation && !currentStatus)) {
-        resolvedStatus = AnnotationResultStatus.ANNOTATED;
+      if (
+        currentStatus === AnnotationResultStatus.NO_ANNOTATION ||
+        currentStatus === AnnotationResultStatus.NOT_APPLICABLE
+      ) {
+        resolvedStatus = currentStatus;
       } else {
         const selectedStatus = await confirmEmptyAnnotationStatus();
         if (!selectedStatus) return false;
@@ -1033,6 +1036,15 @@ export default function LabelStudioTextEditor() {
     [segmentTreeData]
   );
 
+  const inProgressSegmentedCount = useMemo(() => {
+    if (tasks.length === 0) return 0;
+    return tasks.reduce((count, item) => {
+      const summary = resolveSegmentSummary(item);
+      if (!summary) return count;
+      return summary.done < summary.total ? count + 1 : count;
+    }, 0);
+  }, [tasks]);
+
   const handleSegmentSelect = useCallback((keys: Array<string | number>) => {
     const [first] = keys;
     if (first === undefined || first === null) return;
@@ -1214,8 +1226,13 @@ export default function LabelStudioTextEditor() {
           className="border-r border-gray-200 bg-gray-50 flex flex-col transition-all duration-200 min-h-0"
           style={{ width: sidebarCollapsed ? 0 : 240, overflow: "hidden" }}
         >
-          <div className="px-3 py-2 border-b border-gray-200 bg-white font-medium text-sm">
-            文件列表
+          <div className="px-3 py-2 border-b border-gray-200 bg-white font-medium text-sm flex items-center justify-between gap-2">
+            <span>文件列表</span>
+            {segmented && (
+              <Tag color="orange" style={{ margin: 0 }}>
+                标注中 {inProgressSegmentedCount}
+              </Tag>
+            )}
           </div>
           <div className="flex-1 min-h-0 overflow-auto">
             <List