feature/#26-di-setup
develop
- Infrastructure/DependencyInjection.cs: AddInfrastructure() 확장 메서드 - Application/DependencyInjection.cs: AddApplication() 확장 메서드 - API/Extensions/ApplicationBuilderExtensions.cs: UseMiddlewarePipeline() 확장 메서드 - Program.cs 정리 (DI/파이프라인 분리) Closes #26