Add asset proxy feature for resource URLs

Introduces asset proxy configuration and services to enable replacement of osu! resource URLs with custom domains. Updates API endpoints and caching services to process and rewrite resource URLs when asset proxy is enabled. Adds documentation and environment variables for asset proxy setup.

app/config.py

@@ -167,6 +167,13 @@ class Settings(BaseSettings):
     user_cache_max_preload_users: int = 200  # 最多预加载的用户数量
     user_cache_concurrent_limit: int = 10  # 并发缓存用户的限制
 
+    # 资源代理设置
+    enable_asset_proxy: bool = True  # 启用资源代理功能
+    custom_asset_domain: str = "g0v0.top"  # 自定义资源域名
+    asset_proxy_prefix: str = "assets-ppy"  # assets.ppy.sh的自定义前缀
+    avatar_proxy_prefix: str = "a-ppy"  # a.ppy.sh的自定义前缀
+    beatmap_proxy_prefix: str = "b-ppy"  # b.ppy.sh的自定义前缀
+
     # 反作弊设置
     suspicious_score_check: bool = True
     banned_name: list[str] = [