Actualize the project documentation, add latest changes in the backend architecture

https://github.com/5sControl/QA_documentation/blob/main/Diagram%20fiveScontrol(V%200.3.6).png

The issue points to a diagram in the QA_documentation repository. First, examine the linked PNG file to understand the current architecture diagram (version 0.3.6). Then, compare it with the actual backend code in this repository to identify what has changed. Update the project's main documentation (likely README or docs/) to reflect the latest backend architecture.

索引モデルが issue の本文から書いたものです。