feat(player): docked queue overlay with reorder, remove, jump, and clear-upcoming

Add a Queue toggle to the docked player bar opening a centered editable queue
overlay. New additive QueueService.ClearUpcoming keeps the playing track while
dropping the rest. Current track is non-removable.

DeepDrftPublic.Client/Controls/QueueList.razor

@@ -113,7 +113,10 @@
                 <MudIcon Icon="@Icons.Material.Filled.GraphicEq" Size="Size.Small"
                          Color="Color.Primary" Class="deepdrft-queue-nowplaying"/>
             }
-            @if (Editable)
+            @* The current track cannot be removed (OQ3/OQ11): the queue empties only organically as the
+               current ends with nothing after it. Suppress the × on the current row only — reorder of the
+               current track is still allowed. *@
+            @if (Editable && !isCurrent)
             {
                 <MudIconButton Icon="@Icons.Material.Filled.Close" Size="Size.Small"
                                Class="deepdrft-queue-remove" aria-label="Remove from queue"