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/AudioPlayerBar/AudioPlayerBar.razor

@@ -45,7 +45,7 @@ else
                 @* Fixed (embed) queue panel (§4 / AC5). A release embed shows the up-next inline below the
                    controls as a read-only list (Editable=false → no drag handles, no remove buttons; C3).
                    Jump-to-track is still allowed (OQ2) — routed through the same OnQueueJump as the docked
-                   overlay, which calls PlayRelease (clearing IsArmed if the embed was armed-but-not-started).
+                   overlay, which calls JumpTo (moves the pointer and streams the row, clearing IsArmed).
                    Gated on ShowFixedPanel so a single-track embed (empty queue) stays panel-free (UC6). The
                    Queue button collapses/expands this panel (OQ1 Option A); collapse hides it and posts the
                    shrunken height to the host iframe. *@

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

@@ -85,7 +85,13 @@ public partial class AudioPlayerBar : ComponentBase, IAsyncDisposable
     // Gated on Fixed + non-empty so single-track embeds keep their compact, panel-free bar (UC6).
     private bool ShowFixedPanel => Fixed && HasQueue;
 
-    private IReadOnlyList<TrackDto> QueueItems => QueueService?.Items ?? [];
+    // Snapshot the live queue into a NEW list every render. QueueService.Items returns the service's
+    // backing list by reference, so passing it straight through means Blazor parameter diffing sees an
+    // unchanged reference after an in-place Clear/remove/reorder and the child (QueueList /
+    // MudDropContainer) keeps its stale snapshot until reopened (bug #4). Materializing a fresh list per
+    // access forces the parameter to change identity on every mutation, so the panel re-flows immediately.
+    private IReadOnlyList<TrackDto> QueueItems =>
+        QueueService is null ? [] : QueueService.Items.ToList();
     private int QueueCurrentIndex => QueueService?.CurrentIndex ?? -1;
 
     // Fixed-mode panel collapse state (OQ1 Option A). Default expanded so a release embed shows the
@@ -189,12 +195,14 @@ public partial class AudioPlayerBar : ComponentBase, IAsyncDisposable
 
     private void ClearUpcoming() => QueueService?.ClearUpcoming();
 
-    // Jump reuses the existing "play from index" semantics (OQ2). This is the one queue action that
-    // touches playback — it streams the chosen track via the player.
+    // Jump to a row already in the queue. Under the deque model PlayRelease prepends (it is a PLAY,
+    // not an in-place seek), so a jump cannot route through it without duplicating the queue. JumpTo
+    // moves the pointer to the chosen row and streams it once — preserving deque order. This is the one
+    // queue action besides PLAY/skip that touches playback.
     private async Task OnQueueJump(int index)
     {
         if (QueueService == null) return;
-        await QueueService.PlayRelease(QueueService.Items, index);
+        await QueueService.JumpTo(index);
     }
 
     protected override async Task OnAfterRenderAsync(bool firstRender)