perf(backend): 大纲卷过滤下推 DB WHERE——list_for_project 加 volume 参数

GET /outline?volume=N 原在端点 Python 侧过滤全部章节；现把 volume 条件下推到
OutlineRepo.list_for_project 的 DB WHERE，只查该卷行（少读多余卷 + 语义正确）。
Protocol/SqlOutlineRepo/各 OutlineRepo fake 同步加 keyword-only volume；补 repo 级
下推断言测试。向后兼容：不传 volume 仍返回全部（默认 None）。

packages/core/tests/test_memory.py

@@ -44,8 +44,11 @@ class FakeOutlineRepo:
     async def get(self, project_id: uuid.UUID, chapter_no: int) -> OutlineView | None:
         return self.rows.get(chapter_no)
 
-    async def list_for_project(self, project_id: uuid.UUID) -> list[OutlineView]:
-        return [self.rows[k] for k in sorted(self.rows)]
+    async def list_for_project(
+        self, project_id: uuid.UUID, *, volume: int | None = None
+    ) -> list[OutlineView]:
+        rows = [self.rows[k] for k in sorted(self.rows)]
+        return [v for v in rows if volume is None or v.volume == volume]
 
 
 @dataclass

packages/core/ww_core/domain/repositories.py

@@ -115,7 +115,11 @@ class ProjectSpecView(BaseModel):
 class OutlineRepo(Protocol):
     async def get(self, project_id: uuid.UUID, chapter_no: int) -> OutlineView | None: ...
 
-    async def list_for_project(self, project_id: uuid.UUID) -> list[OutlineView]: ...
+    async def list_for_project(
+        self, project_id: uuid.UUID, *, volume: int | None = None
+    ) -> list[OutlineView]:
+        """按 chapter_no 升序返回。`volume` 非 None 时**在 DB WHERE 下推**只取该卷。"""
+        ...
 
 
 class CharacterRepo(Protocol):

packages/core/ww_core/memory/sql_repositories.py

@@ -56,12 +56,13 @@ class SqlOutlineRepo:
             foreshadow_windows=list(row.foreshadow_windows or []),
         )
 
-    async def list_for_project(self, project_id: uuid.UUID) -> list[OutlineView]:
-        rows = (
-            await self._s.execute(
-                select(Outline).where(Outline.project_id == project_id).order_by(Outline.chapter_no)
-            )
-        ).scalars()
+    async def list_for_project(
+        self, project_id: uuid.UUID, *, volume: int | None = None
+    ) -> list[OutlineView]:
+        stmt = select(Outline).where(Outline.project_id == project_id)
+        if volume is not None:
+            stmt = stmt.where(Outline.volume == volume)
+        rows = (await self._s.execute(stmt.order_by(Outline.chapter_no))).scalars()
         return [
             OutlineView(
                 volume=r.volume,