When using FS storage for uploads, use `/uploads` as the prefix instead of `/assets`

[ThisIsMissEm]

Currently we use /assets for legacy reasons, but it really isn't the static assets but rather the user-generated content: https://github.com/fedify-dev/hollo/blob/main/src/index.tsx#L24

In order to change this we would need to:

• redirect /assets/* to /uploads/*
• serve uploads from /uploads

We could also change this to /media or something if that sounds better?

We may also want to include documentation on how to server uploads directly from nginx or similar.