nix/docs: update stub-eval + index text to services.hyperhive.* namespace

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.

nix/docs.nix

@@ -288,7 +288,7 @@ let
       echo '<h1>hyperhive — nix options reference</h1>'
       echo '<p>Auto-generated from the <a href="${forgeRoot}">hyperhive flake</a>. Two reading paths:</p>'
       echo '<h3><a href="./host.html">host options</a></h3>'
-      echo '<p>Options exposed by <code>hyperhive.nixosModules.default</code> to operator host configurations: <code>services.hive-c0re.*</code>, <code>hyperhive.domain</code>, <code>hyperhive.forge.*</code>, <code>hyperhive.matrix.*</code>.</p>'
+      echo '<p>Options exposed by <code>hyperhive.nixosModules.default</code> to operator host configurations: <code>services.hyperhive.{enable,domain,c0re,forge,matrix,gateway}.*</code>.</p>'
       echo '<h3><a href="./agent.html">agent options</a></h3>'
       echo '<p>Per-agent options declared in <code>nix/templates/harness-base.nix</code> and visible from every <code>agent.nix</code>: <code>hyperhive.model</code>, <code>hyperhive.allowedRecipients</code>, <code>hyperhive.extraMcpServers</code>, <code>hyperhive.frontend.*</code>, <code>hyperhive.forge.*</code>, <code>hyperhive.matrix.*</code>, <code>hyperhive.gui.*</code>.</p>'
       echo '<h3>Regenerate</h3>'