feat: Phase 17.3 — Fixed embed queue panel with collapse/expand iframe resize (OQ1 Option A)

Read-only inline queue panel below the release embed's player bar; row-jump reuses PlayRelease. ForRelease mints a taller iframe plus a postMessage resize listener for the collapse toggle; ForTrack unchanged.

DeepDrftPublic.Client/Controls/AudioPlayerBar/AudioPlayerBar.razor

@@ -26,7 +26,7 @@ else
                                          SkipNext="@SkipNext"
                                          SkipPrevious="@SkipPrevious"
                                          ShowQueueButton="ShowQueueButton"
-                                         QueueOpen="_queueOpen"
+                                         QueueOpen="QueueButtonOpen"
                                          QueueToggle="@ToggleQueue"
                                          Class="transport-zone"/>
 
@@ -42,6 +42,23 @@ else
                                     Class="seek-zone"/>
                 </div>
 
+                @* 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).
+                   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. *@
+                @if (ShowFixedPanel && _fixedPanelOpen)
+                {
+                    <div class="deepdrft-queue-embed-panel">
+                        <QueueList Items="QueueItems"
+                                   CurrentIndex="QueueCurrentIndex"
+                                   Editable="false"
+                                   OnJump="@OnQueueJump"/>
+                    </div>
+                }
+
                 @* Minimize / close — positioned absolutely top-right *@
                 @if (!Fixed)
                 {
@@ -62,8 +79,8 @@ else
 
         @* Docked queue overlay (Phase 17 §3.2). MudOverlay portals to the body, so its position here in
            the dock subtree does not affect its screen-centered rendering. Only mounted in docked mode —
-           the Fixed embed gets its own inline panel in a later wave. *@
-        @if (ShowQueueButton)
+           the Fixed embed renders its own inline panel inside the surface above. *@
+        @if (ShowDockedOverlay)
         {
             <QueueOverlay Visible="_queueOpen"
                           Items="QueueItems"