Add Service DoM dashboard policy page

Mirror the repo-doi/workstream-dod Observable policy pages for service-dom:
read/edit view backed by GET/PUT /policy/service-dom. Add it to the Policies
nav section and the State Hub reference doc. Builds clean (62 pages).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

dashboard/observablehq.config.js

@@ -44,6 +44,7 @@ export default {
       open: false,
       pages: [
         { name: "Repository DoI",  path: "/policy/repo-doi" },
+        { name: "Service DoM",     path: "/policy/service-dom" },
         { name: "Workstream DoD", path: "/policy/workstream-dod" },
       ],
     },