系统设计方法论附录中的冷启动练习资源建议

Hi Sanbu, I have carefully reviewed docs/de-de/appendix/6-architecture-and-system-design/system-design-methodology.md. The System Design Appendix organizes requirements clarification, capacity estimation, APIs, data models, high-level architecture, and bottleneck analysis into a repeatable methodology, rather than just presenting the final architecture diagram.