feat(mix-visualizer): gate knob controls with Blazor @if in TopContent band; drop CSS collapse, glass, and TopRowCenter slot

DeepDrftPublic.Client/Controls/ReleaseDetailScaffold.razor.cs

@@ -25,21 +25,13 @@ public partial class ReleaseDetailScaffold : ComponentBase
     [Parameter] public string BackLabel { get; set; } = "Archive";
 
     /// <summary>
-    /// Optional medium-specific content rendered between the back link and the masthead — the "below
-    /// the back button, above the details" band. The Mix detail page uses it for the visualizer
-    /// controls row; other media leave it null.
+    /// Optional medium-specific content rendered as its own full-width band between the back/action top
+    /// row and the masthead — the "below the back button, above the details" band. The Mix detail page
+    /// uses it for the visualizer knob row (gated by Blazor on the lava-lamp toggle); other media leave
+    /// it null.
     /// </summary>
     [Parameter] public RenderFragment? TopContent { get; set; }
 
-    /// <summary>
-    /// Optional affordance rendered in the center of the top row, between the back link (left) and
-    /// <see cref="TopRightAction"/> (right). The Mix detail page uses it for the in-flow visualizer-
-    /// controls container that grows in place between the back link and the lava-lamp toggle (§7b);
-    /// other media leave it null, so the SpaceBetween row collapses the center and renders the back
-    /// link alone. Variance rides the slot, never a flag (Phase 9 §5.3).
-    /// </summary>
-    [Parameter] public RenderFragment? TopRowCenter { get; set; }
-
     /// <summary>
     /// Optional action rendered at the top-right of the container, on the same SpaceBetween row as the
     /// back link (back link left, action right). The Mix detail page uses it for the lava-lamp