Footer shows “undefined” link and incorrect GitHub commit URL

The footer displays a link with the text undefined, and the generated URL points to /commit/undefined. This happens because import.meta.env.VITE_GIT_SHA is not defined during the build.

<img width="737" height="1282" alt="Image" src="https://github.com/user-attachments/assets/1364722a-8360-4b44-8964-2d2267889b49" />