AI: Central SiteMap controls released vs in-development pages

- New SiteMap registry: single source of truth for page visibility.
  Fail-closed: unlisted or Released=false pages are hidden.
- NavMenu renders nav links from SiteMap.NavEntries (galaxy only).
- New Components/ReleaseGuard wraps the Router's Found template:
  unreleased routes redirect to /galaxy (covers direct URLs).
- Galaxy map released; system/mastery detail dossiers released but
  not in nav (linked from the map); Home, indexes, Units hidden.
- Brand logo now links to /galaxy.

ZeroSpace/ZeroSpace.Web/App.razor

@@ -1,6 +1,6 @@
 <Router AppAssembly="@typeof(App).Assembly" NotFoundPage="typeof(Pages.NotFound)">
     <Found Context="routeData">
-        <RouteView RouteData="@routeData" DefaultLayout="@typeof(MainLayout)"/>
+        <ReleaseGuard RouteData="@routeData"/>
         <FocusOnNavigate RouteData="@routeData" Selector="h1"/>
     </Found>
 </Router>