fix(seo): escape inline JSON-LD, per-release byArtist, soft-404 + env-gated noindex

Escape </>& in JSON-LD body to kill script-breakout; byArtist now uses the release artist; detail-page not-found branches emit noindex; default robots gated to Production via a PersistentState SeoEnvironment bridge.

DeepDrftPublic.Client/Controls/SeoHead.razor

@@ -1,5 +1,6 @@
 @using DeepDrftPublic.Client.Common
 @inject SeoOptions Seo
+@inject SeoEnvironment SeoEnv
 @inject NavigationManager Nav
 
 @*
@@ -83,7 +84,9 @@
     {
         _fullTitle = $"{Model.Title} · {Seo.TitleSuffix}";
         _description = string.IsNullOrWhiteSpace(Model.Description) ? Seo.DefaultDescription : Model.Description;
-        _robots = string.IsNullOrWhiteSpace(Model.Robots) ? Seo.DefaultRobots : Model.Robots;
+        // Default robots is environment-gated (non-production → noindex,nofollow) so beta/staging is never
+        // crawled; an explicit per-page Robots still wins (e.g. the 404's / soft-404's noindex,follow).
+        _robots = string.IsNullOrWhiteSpace(Model.Robots) ? SeoEnv.DefaultRobots : Model.Robots;
         _ogType = OgTypeString(Model.OgType);
 
         // Canonical: BaseUrl + the model's path, defaulting to the current relative path. The origin is