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/service/ranking_cache_service.py

@@ -15,6 +15,7 @@ from app.database.statistics import UserStatistics, UserStatisticsResp
 from app.log import logger
 from app.models.score import GameMode
 from app.utils import utcnow
+from app.service.asset_proxy_service import get_asset_proxy_service
 
 from redis.asyncio import Redis
 from sqlmodel import col, select
@@ -283,6 +284,15 @@ class RankingCacheService:
                     ranking_data = []
                     for statistics in statistics_data:
                         user_stats_resp = await UserStatisticsResp.from_db(statistics, session, None, include)
+                        
+                        # 应用资源代理处理
+                        if settings.enable_asset_proxy:
+                            try:
+                                asset_proxy_service = get_asset_proxy_service()
+                                user_stats_resp = await asset_proxy_service.replace_asset_urls(user_stats_resp)
+                            except Exception as e:
+                                logger.warning(f"Asset proxy processing failed for ranking cache: {e}")
+                        
                         # 将 UserStatisticsResp 转换为字典，处理所有序列化问题
                         user_dict = json.loads(user_stats_resp.model_dump_json())
                         ranking_data.append(user_dict)