site: missing icon for filebrowser

# Problem

Our [filebrowser module](https://github.com/coder/modules/blob/f5ab7995d145971d25766ba826901b7eac4c5227/filebrowser/main.tf#L89) references `/icon/filebrowser.svg` but this currently does not exist in our codebase, resulting in a messy-looking filebrowser icon:

![Image](https://github.com/user-attachments/assets/888c7f41-b4a0-44ea-babc-39850e7e3207)
