fix(mix-visualizer): move seven-knob controls in-flow between back link and lava lamp (Phase 10 reframe §7b)

DeepDrftPublic.Client/Controls/ReleaseDetailScaffold.razor.cs

@@ -31,6 +31,15 @@ public partial class ReleaseDetailScaffold : ComponentBase
     /// </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