Cleanup of image folders

https://github.com/matrix-org/matrix.org/tree/main/static has way too many image folders for historic reasons.

I guess the best would be to reorganize, move images next to their posts, and then set up redirects.

Start by inventorying the image folders under static and tracing how the website serves paths for existing posts. Review the site's redirect configuration or routing entry points before proposing a layout. Done means the image structure is intentionally reorganized and existing image URLs continue to resolve through redirects.

Written by the indexing model from the issue text.