feat(queue): two-level deque model — PLAY prepends, add appends, last-track-end empties

Fixes five queue bugs: Playlist relabel, last-track-empties, dormant-seed-from-player on first add, immediate panel reactivity, and front/back deque semantics. Adds JumpTo for row jumps.

DeepDrftPublic.Client/Controls/StreamNowButton.razor

@@ -27,6 +27,7 @@
     [Parameter] public string LoadingLabel { get; set; } = "Finding a track…";
     [Parameter] public EventCallback OnStreamStarted { get; set; }
     [CascadingParameter] public IStreamingPlayerService? PlayerService { get; set; }
+    [CascadingParameter] public IQueueService? Queue { get; set; }
     [Inject] public required ITrackDataService TrackData { get; set; }
 
     private bool _streamLoading;
@@ -79,7 +80,12 @@
             _findingTrack = false;
             StateHasChanged();
 
-            if (PlayerService is not null)
+            // PLAY semantics: prepend to the queue's front so a "stream now" track becomes current and
+            // any existing queue stays intact behind it. Falls back to a direct stream when the queue
+            // cascade is absent.
+            if (Queue is not null)
+                await Queue.PlayTrack(track);
+            else if (PlayerService is not null)
                 await PlayerService.SelectTrackStreaming(track);
         }
         catch (Exception)