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/Common/SeoOptions.cs

@@ -40,8 +40,9 @@ public sealed record SeoOptions
     /// <summary>The collective's primary genre, used in the MusicGroup JSON-LD node.</summary>
     public string Genre { get; init; } = "Electronic";
 
-    /// <summary>Default robots directive; a page may override (e.g. the 404's <c>noindex,follow</c>).</summary>
-    public string DefaultRobots { get; init; } = "index,follow";
+    // The default robots directive is NOT a static option — it is environment-gated (Production →
+    // index,follow; non-production → noindex,nofollow) via SeoEnvironment so the beta/staging site is
+    // never crawled. A page's explicit SeoModel.Robots still overrides that default.
 
     /// <summary>
     /// Public social profile URLs for the MusicGroup <c>sameAs</c> array (OQ3). Instagram only —