feat: 更新章节查询逻辑以仅返回活跃章节

- 修改章节查询语句，确保只查找标记为活跃的章节，避免更新已清除的章节。
- 相关注释更新以反映新的逻辑，提升代码可读性。

api/tasks/memoir_tasks.py

@@ -212,10 +212,11 @@ def process_memoir_segments(self, user_id: str, segment_ids: List[str]):
                 combined_text = "\n\n".join(segment_texts)
                 source_ids = [seg.id for seg in stage_segments]
                 
-                # 查找或创建章节
+                # 查找 active 章节（被清除的章节不继续更新，而是创建新的）
                 stmt_chapter = select(Chapter).where(
                     Chapter.user_id == user_id,
                     Chapter.category == stage,
+                    Chapter.is_active == True,
                 )
                 result_chapter = db.execute(stmt_chapter)
                 chapter = result_chapter.scalar_one_or_none()
@@ -340,10 +341,11 @@ def generate_chapter_content(self, user_id: str, stage: str, new_content: str):
         try:
             llm = llm_service.get_llm()
             
-            # 查找章节
+            # 查找 active 章节（被清除的章节不继续更新，而是创建新的）
             stmt = select(Chapter).where(
                 Chapter.user_id == user_id,
                 Chapter.category == stage,
+                Chapter.is_active == True,
             )
             result = db.execute(stmt)
             chapter = result.scalar_one_or_none()