Add updated auth diagrams

Our auth diagrams are no longer up-to-date with our current auth flow. We need updated versions of sample auth flows in the README.

Below is a modern example of the auth flow. The new charts should be generic in the way that services are generically named to show a user how the auth flow with auth.abandontech.cloud will fit into their applications. We may wish to include two versions--one version for a server-side rendered application, and an additional version for an application with separate front/backends. The differences between these two are subtle, but I believe it is worth illustrating both.

Diagrams should be clearly labeled and color-coded similarly to the existing ones in the readme


检查 README 中现有的 auth 图表以及 issue 中提供的示例图片。创建更新后的图表，用于说明服务器端渲染应用和前端/后端分离应用的通用 auth 流程，并与当前图表的样式和颜色编码保持一致。确保图表标注清晰，并符合项目的文档标准。

由索引模型根据 Issue 内容生成。