feature: 新增支持拆书自选保留章节数，或者整本拆书功能

backend/app/api/book_import.py

@@ -15,6 +15,7 @@ from app.schemas.book_import import (
     BookImportPreviewResponse,
     BookImportRetryRequest,
     BookImportTaskCreateResponse,
+    BookImportTaskCreateRequest,
     BookImportTaskStatusResponse,
 )
 from app.services.book_import_service import book_import_service
@@ -33,6 +34,8 @@ async def create_book_import_task(
     project_id: str | None = Form(default=None, description="兼容参数：当前版本固定新建项目，不支持传入"),
     create_new_project: bool = Form(default=True, description="兼容参数：当前版本仅支持 true"),
     import_mode: str = Form(default="append", description="导入模式：append/overwrite"),
+    extract_mode: str = Form(default="tail", description="解析范围：tail=截取末章，full=整本"),
+    tail_chapter_count: int = Form(default=10, description="当 extract_mode=tail 时，截取末尾章节数，需为5的倍数；超过50按整本拆处理"),
 ):
     user_id = getattr(request.state, "user_id", None)
     if not user_id:
@@ -44,11 +47,26 @@ async def create_book_import_task(
     if import_mode not in {"append", "overwrite"}:
         raise HTTPException(status_code=400, detail="import_mode 仅支持 append 或 overwrite")
 
+    if extract_mode not in {"tail", "full"}:
+        raise HTTPException(status_code=400, detail="extract_mode 仅支持 tail 或 full")
+    if tail_chapter_count < 5:
+        raise HTTPException(status_code=400, detail="tail_chapter_count 不能小于 5")
+    if tail_chapter_count % 5 != 0:
+        raise HTTPException(status_code=400, detail="tail_chapter_count 必须是 5 的倍数")
+
+    if tail_chapter_count > 50:
+        extract_mode = "full"
+
     if project_id:
         raise HTTPException(status_code=400, detail="当前仅支持新建项目导入，不支持指定 project_id")
     if not create_new_project:
         raise HTTPException(status_code=400, detail="当前仅支持新建项目导入")
 
+    create_payload = BookImportTaskCreateRequest(
+        extract_mode=extract_mode,
+        tail_chapter_count=tail_chapter_count,
+    )
+
     content = await file.read()
     if len(content) > MAX_TXT_SIZE:
         raise HTTPException(status_code=413, detail="文件大小超过 50MB 限制")
@@ -60,6 +78,8 @@ async def create_book_import_task(
         project_id=None,
         create_new_project=True,
         import_mode=import_mode,
+        extract_mode=create_payload.extract_mode,
+        tail_chapter_count=create_payload.tail_chapter_count,
     )
     return task