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/SiteMap.cs

@@ -0,0 +1,51 @@
+using Microsoft.AspNetCore.Components.Routing;
+
+namespace ZeroSpace.Web;
+
+/// <summary>
+/// Single source of truth for which pages exist, which are released,
+/// and which appear in navigation. New pages are hidden until explicitly
+/// released here (fail-closed): anything not listed, or listed with
+/// Released=false, redirects to the galaxy map via <see cref="Components.ReleaseGuard"/>.
+/// </summary>
+public static class SiteMap
+{
+    public sealed record Entry(
+        Type Page,
+        string Title,
+        string Href,
+        string IconCss,
+        string? Badge,
+        NavLinkMatch Match,
+        bool Released,
+        bool ShowInNav);
+
+    public static readonly IReadOnlyList<Entry> Entries =
+    [
+        // The releasable surface.
+        new(typeof(Pages.Galaxy), "Galaxy Map", "galaxy", "bi bi-galaxy-nav-menu", "MAP",
+            NavLinkMatch.Prefix, Released: true, ShowInNav: true),
+
+        // Detail dossiers: part of the galaxy experience (linked from the map),
+        // but not top-level navigation destinations.
+        new(typeof(Pages.StarSystemDetail), "System Dossier", "StarSystem", "bi bi-star-systems-nav-menu", null,
+            NavLinkMatch.Prefix, Released: true, ShowInNav: false),
+        new(typeof(Pages.SystemMasteryDetail), "Mastery Dossier", "SystemMastery", "bi bi-masteries-nav-menu", null,
+            NavLinkMatch.Prefix, Released: true, ShowInNav: false),
+
+        // In-development pages: hidden from nav and unreachable by URL for now.
+        new(typeof(Pages.Home), "Home", "", "bi bi-house-door-fill-nav-menu", null,
+            NavLinkMatch.All, Released: false, ShowInNav: false),
+        new(typeof(Pages.StarSystemIndex), "Star Systems", "StarSystem", "bi bi-star-systems-nav-menu", null,
+            NavLinkMatch.Prefix, Released: false, ShowInNav: false),
+        new(typeof(Pages.SystemMasteryIndex), "Masteries", "SystemMastery", "bi bi-masteries-nav-menu", null,
+            NavLinkMatch.Prefix, Released: false, ShowInNav: false),
+        new(typeof(Pages.Units), "Units", "units", "bi bi-units-nav-menu", null,
+            NavLinkMatch.Prefix, Released: false, ShowInNav: false),
+    ];
+
+    public static IEnumerable<Entry> NavEntries => Entries.Where(e => e.Released && e.ShowInNav);
+
+    public static bool IsReleased(Type pageType) =>
+        Entries.FirstOrDefault(e => e.Page == pageType)?.Released ?? false;
+}