feat(public): add Theater Mode to release detail pages

Toggle left of the lava popover hides release content so the visualizer fills
the surface; player bar grows to carry the playing release's cover, title, and
share. State on WaveformVisualizerControlState; pages and bar observe it.

DeepDrftPublic.Client/Controls/AudioPlayerBar/AudioPlayerBar.razor.cs

@@ -16,12 +16,18 @@ public partial class AudioPlayerBar : ComponentBase, IAsyncDisposable
 
     [Inject] private IJSRuntime JsRuntime { get; set; } = default!;
 
+    // Theater Mode (Phase 20). Property-injected (no constructor growth) so the bar can read
+    // TheaterMode to mount the "now showing" band and re-render when the flag flips. The toggle lives on
+    // the detail pages; the bar only observes — single source, multiple observers (§6).
+    [Inject] private WaveformVisualizerControlState VisualizerControlState { get; set; } = default!;
+
     private bool _isMinimized = true;
     private bool _isSeeking = false;
     private double _seekPosition = 0;
     private bool _queueOpen = false;
     private IStreamingPlayerService? _subscribedService;
     private IQueueService? _subscribedQueue;
+    private bool _subscribedToVisualizerState;
 
     // Spacer-height bridge: the expanded dock is position:fixed, so MainLayout's
     // spacer reserves its space. We mirror this element's live height into a CSS
@@ -143,8 +149,19 @@ public partial class AudioPlayerBar : ComponentBase, IAsyncDisposable
             QueueService.QueueChanged += OnQueueChanged;
             _subscribedQueue = QueueService;
         }
+
+        // Theater Mode (Phase 20 §7): re-render the bar when TheaterMode flips so the "now showing" band
+        // appears/disappears. VisualizerControlState is injected (one stable scoped instance per session),
+        // so the subscribe is once-only — same idempotent subscribe-here / unsubscribe-on-dispose shape.
+        if (!_subscribedToVisualizerState)
+        {
+            VisualizerControlState.Changed += OnVisualizerStateChanged;
+            _subscribedToVisualizerState = true;
+        }
     }
 
+    private void OnVisualizerStateChanged() => InvokeAsync(StateHasChanged);
+
     private void OnPlayerStateChanged() => InvokeAsync(StateHasChanged);
 
     private void OnQueueChanged()
@@ -402,6 +419,12 @@ public partial class AudioPlayerBar : ComponentBase, IAsyncDisposable
             _subscribedQueue = null;
         }
 
+        if (_subscribedToVisualizerState)
+        {
+            VisualizerControlState.Changed -= OnVisualizerStateChanged;
+            _subscribedToVisualizerState = false;
+        }
+
         if (_spacerModule is not null)
         {
             try