Automatically render relevant markdown documents next to README as tabs.

### Feature Description

Noticed that on GH some of the markdown in the root directory are rendered into different tabs next to the README, might be useful to implement the same on Gitea

### Screenshots

<img width="919" height="265" alt="Image" src="https://github.com/user-attachments/assets/9635f49e-31f6-4c43-a877-54146f5ffc8b" />