feat(player): add IQueueService orchestrating album playback above the single-slot player (P11 11.F)

Queue owns ordered tracks, current index, skip-fwd/back, and auto-advance via the player's TrackEnded hook; binds through Attach (no ctor growth, no service-locator). Player-bar skip controls; empty-queue play unchanged. Adds QueueService unit tests.

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

@@ -9,6 +9,7 @@ namespace DeepDrftPublic.Client.Controls.AudioPlayerBar;
 public partial class AudioPlayerBar : ComponentBase, IAsyncDisposable
 {
     [CascadingParameter] public IStreamingPlayerService? PlayerService { get; set; }
+    [CascadingParameter] public IQueueService? QueueService { get; set; }
     [Parameter] public bool Fixed { get; set; } = false;
 
     [Parameter] public EventCallback<bool> OnMinimized { get; set; }
@@ -19,6 +20,7 @@ public partial class AudioPlayerBar : ComponentBase, IAsyncDisposable
     private bool _isSeeking = false;
     private double _seekPosition = 0;
     private IStreamingPlayerService? _subscribedService;
+    private IQueueService? _subscribedQueue;
 
     // 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
@@ -48,6 +50,11 @@ public partial class AudioPlayerBar : ComponentBase, IAsyncDisposable
     private double LoadProgress => PlayerService?.LoadProgress ?? 0;
     private string? ErrorMessage => PlayerService?.ErrorMessage;
 
+    // Skip affordances reflect live queue state. With no queue (null) or an empty queue both are
+    // false, so the buttons sit disabled and the bar behaves exactly as it did before the queue.
+    private bool HasNext => QueueService?.HasNext ?? false;
+    private bool HasPrevious => QueueService?.HasPrevious ?? false;
+
     /// <summary>
     /// Display time - shows seek position while dragging, otherwise current playback time.
     /// </summary>
@@ -76,10 +83,35 @@ public partial class AudioPlayerBar : ComponentBase, IAsyncDisposable
             PlayerService.StateChanged += OnPlayerStateChanged;
             _subscribedService = PlayerService;
         }
+
+        // The queue cascade is also IsFixed, so re-render the skip affordances off its own
+        // change signal — same posture as the player StateChanged subscription above.
+        if (QueueService != null && !ReferenceEquals(QueueService, _subscribedQueue))
+        {
+            if (_subscribedQueue != null)
+                _subscribedQueue.QueueChanged -= OnQueueChanged;
+
+            QueueService.QueueChanged += OnQueueChanged;
+            _subscribedQueue = QueueService;
+        }
     }
 
     private void OnPlayerStateChanged() => InvokeAsync(StateHasChanged);
 
+    private void OnQueueChanged() => InvokeAsync(StateHasChanged);
+
+    private async Task SkipNext()
+    {
+        if (QueueService == null) return;
+        await QueueService.Next();
+    }
+
+    private async Task SkipPrevious()
+    {
+        if (QueueService == null) return;
+        await QueueService.Previous();
+    }
+
     protected override async Task OnAfterRenderAsync(bool firstRender)
     {
         // Only the docked, expanded shape needs a spacer: the Fixed embed is