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/Pages/MixDetail.razor

@@ -100,10 +100,13 @@ else
     protected override string PersistKey => "mix-detail";
 
     [CascadingParameter] public IStreamingPlayerService? PlayerService { get; set; }
+    [CascadingParameter] public IQueueService? Queue { get; set; }
 
     // The hero now carries the play affordance (the scaffold's header is suppressed), so the
     // play-toggle is wired here directly — mirroring SessionDetail. Toggle if this track is already
-    // active, otherwise start a fresh stream.
+    // active, otherwise PLAY it: prepend to the queue's front (deque PLAY semantics) so it becomes
+    // current and the existing queue stays intact behind it. Falls back to a direct stream when the
+    // queue cascade is absent (prerender / non-interactive).
     private async Task PlayTrack()
     {
         var track = ViewModel.Track;
@@ -114,6 +117,10 @@ else
         {
             await PlayerService.TogglePlayPause();
         }
+        else if (Queue is not null)
+        {
+            await Queue.PlayTrack(track);
+        }
         else
         {
             await PlayerService.SelectTrackStreaming(track);