two stale spots in `nix/docs.nix` that #622 didn't catch:
- the stub NixOS eval was force-disabling `hyperhive.{forge,matrix}.enable`
on the old paths, which fail eval post-#615 (`The option `hyperhive'
does not exist`)
- the rendered index page text still listed the old namespace shape
both updated to use `services.hyperhive.*` consistently. necessary on
this branch for `nix flake check` to pass; the same fix lives on PR
a no-op.
7ab3b125ec