feat：新增演示

app/services/screens.py

@@ -428,6 +428,21 @@ class ScreenService:
             deleted=deleted,
         )
 
+    async def list_demo(self, owner_id: int, limit: int) -> list[ScreenRecord]:
+        """演示账号下没删除的大屏（最近修改在前），带页面"""
+        summaries, _ = await self._store.search(
+            owner_id,
+            keyword=None,
+            status=None,
+            sort="updated_at",
+            descending=True,
+            limit=limit,
+            offset=0,
+            deleted=False,
+        )
+        records = [await self._store.get(item.screen_id, owner_id) for item in summaries]
+        return [record for record in records if record is not None]
+
     async def copy_screen(self, screen_id: str, owner_id: int, name: str | None) -> str:
         """只复制草稿和封面，不复制发布状态和历史"""
         source = await self.get(screen_id, owner_id)