refactor(api): use Annotated-style dependency injection

app/dependencies/beatmap_download.py

@@ -1,8 +1,15 @@
 from __future__ import annotations
 
-from app.service.beatmap_download_service import download_service
+from typing import Annotated
+
+from app.service.beatmap_download_service import BeatmapDownloadService, download_service
+
+from fastapi import Depends
 
 
 def get_beatmap_download_service():
     """获取谱面下载服务实例"""
     return download_service
+
+
+DownloadService = Annotated[BeatmapDownloadService, Depends(get_beatmap_download_service)]