fix(ci): .NET 基础镜像改回 mcr.microsoft.com，代理已通且宿主已预拉缓存

Dockerfile.prod

@@ -25,7 +25,7 @@ COPY app/ ./
 RUN pnpm build || npm run build
 
 # 第二阶段：构建后端
-FROM registry.cn-hangzhou.aliyuncs.com/dotnet/sdk:6.0 AS backend-builder
+FROM mcr.microsoft.com/dotnet/sdk:6.0 AS backend-builder
 
 WORKDIR /src
 
@@ -46,7 +46,7 @@ COPY --from=frontend-builder /app/frontend/dist ./app/dist
 RUN dotnet publish dy.net.csproj -c Release -o /app/publish
 
 # 第三阶段：运行镜像
-FROM registry.cn-hangzhou.aliyuncs.com/dotnet/aspnet:6.0 AS final
+FROM mcr.microsoft.com/dotnet/aspnet:6.0 AS final
 
 WORKDIR /app