Routing under `-` causes issues

!20455 (merged) and !21126 (merged) caused some issues when we deployed to GitLab.com.

1. We have rolling deploys on GitLab.com. The old code only knows about the non-- version. That isn't forwards-compatible, which is hard to do, so we have a period of time during the deploy where links might not work, because a page might be served by the new code and then you click on a link and are served the old code. The new code is backwards-compatible.
2. The repository links (particularly for raw) will break any non-redirect-following clients, like curl or gitlab-org/quality/triage-ops!361 (merged).
3. We may need to update Workhorse's upload acceleration to match the new routes.