refactor(annotation): 简化文本标注编辑器的段落管理功能

- 移除段落统计相关的数据结构和缓存逻辑
- 删除段落切换确认对话框和自动保存选项
- 简化段落加载和状态管理流程
- 将段落列表视图替换为简单的进度显示
- 更新API接口以支持单段内容获取
- 重构后端服务实现单段内容查询功能

runtime/datamate-python/app/module/annotation/service/editor.py

@@ -36,8 +36,9 @@ from app.module.annotation.schema.editor import (
     EditorProjectInfo,
     EditorTaskListItem,
     EditorTaskListResponse,
+    EditorTaskSegmentResponse,
     EditorTaskResponse,
-    EditorTaskSegmentsResponse,
+    SegmentDetail,
     SegmentInfo,
     UpsertAnnotationRequest,
     UpsertAnnotationResponse,
@@ -713,18 +714,19 @@ class AnnotationEditorService:
 
         return await self._build_text_task(project, file_record, file_id, segment_index)
 
-    async def get_task_segments(
+    async def get_task_segment(
         self,
         project_id: str,
         file_id: str,
-    ) -> EditorTaskSegmentsResponse:
+        segment_index: int,
+    ) -> EditorTaskSegmentResponse:
         project = await self._get_project_or_404(project_id)
 
         dataset_type = self._normalize_dataset_type(await self._get_dataset_type(project.dataset_id))
         if dataset_type != DATASET_TYPE_TEXT:
             raise HTTPException(
                 status_code=400,
-                detail="当前仅支持 TEXT 项目的段落摘要",
+                detail="当前仅支持 TEXT 项目的段落内容",
             )
 
         file_result = await self.db.execute(
@@ -738,7 +740,12 @@ class AnnotationEditorService:
             raise HTTPException(status_code=404, detail=f"文件不存在或不属于该项目: {file_id}")
 
         if not self._resolve_segmentation_enabled(project):
-            return EditorTaskSegmentsResponse(segmented=False, segments=[], totalSegments=0)
+            return EditorTaskSegmentResponse(
+                segmented=False,
+                segment=None,
+                totalSegments=0,
+                currentSegmentIndex=0,
+            )
 
         text_content = await self._fetch_text_content_via_download_api(project.dataset_id, file_id)
         assert isinstance(text_content, str)
@@ -768,7 +775,12 @@ class AnnotationEditorService:
             len(text or "") > self.SEGMENT_THRESHOLD for text in record_texts
         )
         if not needs_segmentation:
-            return EditorTaskSegmentsResponse(segmented=False, segments=[], totalSegments=0)
+            return EditorTaskSegmentResponse(
+                segmented=False,
+                segment=None,
+                totalSegments=0,
+                currentSegmentIndex=0,
+            )
 
         ann_result = await self.db.execute(
             select(AnnotationResult).where(
@@ -782,16 +794,42 @@ class AnnotationEditorService:
             segment_annotations = self._extract_segment_annotations(ann.annotation)
         segment_annotation_keys = set(segment_annotations.keys())
 
-        segments, _ = self._build_segment_contexts(
+        segments, segment_contexts = self._build_segment_contexts(
             records,
             record_texts,
             segment_annotation_keys,
         )
 
-        return EditorTaskSegmentsResponse(
+        total_segments = len(segment_contexts)
+        if total_segments == 0:
+            return EditorTaskSegmentResponse(
+                segmented=False,
+                segment=None,
+                totalSegments=0,
+                currentSegmentIndex=0,
+            )
+
+        if segment_index < 0 or segment_index >= total_segments:
+            raise HTTPException(
+                status_code=400,
+                detail=f"segmentIndex 超出范围: {segment_index}",
+            )
+
+        segment_info = segments[segment_index]
+        _, _, segment_text, line_index, chunk_index = segment_contexts[segment_index]
+        segment_detail = SegmentDetail(
+            idx=segment_info.idx,
+            text=segment_text,
+            hasAnnotation=segment_info.has_annotation,
+            lineIndex=line_index,
+            chunkIndex=chunk_index,
+        )
+
+        return EditorTaskSegmentResponse(
             segmented=True,
-            segments=segments,
-            totalSegments=len(segments),
+            segment=segment_detail,
+            totalSegments=total_segments,
+            currentSegmentIndex=segment_index,
         )
 
     async def _build_text_task(