feat(theater): full-screen detail body, eased content collapse, playing-release scoping

Detail bodies fill 100vh below the nav so the visualizer reads full-screen; Theater toggle eases page content and the player-bar now-showing panel in/out instead of popping (reduced-motion honored); Theater only applies to the currently-playing release.

DeepDrftPublic.Client/Pages/CutDetail.razor

@@ -37,6 +37,10 @@ else
     var hasYear = release.ReleaseDate is not null;
     var firstTrack = ViewModel.Tracks.Count > 0 ? ViewModel.Tracks[0] : null;
 
+    @* Full-screen content body (Phase 20 Wave 2 §1): the scaffold has no Class param, so a thin wrapper
+       carries the min-height. dd-detail-fill keeps the body >= viewport height (below the nav) so the
+       ambient visualizer reads full-screen and the site footer is pushed below the fold. *@
+    <div class="dd-detail-fill">
     <ReleaseDetailScaffold Title="@release.Title"
                            Artist="@release.Artist"
                            Track="@firstTrack"
@@ -58,17 +62,19 @@ else
                controls over the experience, not release content, so both stay in Theater Mode (§4/OQ4).
                Wrapped so they cluster on the right rather than spreading across the SpaceBetween row. *@
             <div class="dd-detail-top-actions">
-                <TheaterModeToggle />
+                @* Theater toggle only appears when this Cut is the currently-playing release (Phase 20
+                   Wave 2 §3). ShowTheaterToggle folds in the subsystem gate + the release-playing check. *@
+                <TheaterModeToggle Available="ShowTheaterToggle" />
                 @* Lava-lamp icon → popover panel (full parity, §3d-revised). Sits top-right across from the
                    back link, clear of the header's own Play/Share affordances below. *@
                 <WaveformVisualizerControlPopover />
             </div>
         </TopRightAction>
         <Header>
-            @* Theater Mode (Phase 20 §4): the release content is removed from the render — not
-               CSS-hidden — so the visualizer fills the surface. OFF restores it byte-for-byte. *@
-            @if (!VisualizerControlState.TheaterMode)
-            {
+            @* Theater Mode (Phase 20 §4, Wave 2 §2): the release content stays mounted and eases out via
+               a collapsing wrapper so it does not pop — IsContentHidden collapses it to zero height when
+               Theater is on AND this Cut is the playing release. OFF eases it back to its normal layout. *@
+            <div class="dd-theater-collapsible @(IsContentHidden ? "dd-theater-collapsed" : null)">
             @* Header split: meta + Play/Share on the LEFT, bordered cover on the RIGHT (spec §3.1). *@
             <div class="cut-detail-header">
                 <div class="cut-detail-meta">
@@ -127,11 +133,11 @@ else
                     }
                 </div>
             </div>
-            }
+            </div>
         </Header>
         <BodyContent>
-            @if (!VisualizerControlState.TheaterMode)
-            {
+            @* Theater Mode (Wave 2 §2): eased collapse, mirroring the Header region. *@
+            <div class="dd-theater-collapsible @(IsContentHidden ? "dd-theater-collapsed" : null)">
             @* Blurb sits between the header and the track-list divider. *@
             <ReleaseDescription Description="@release.Description" />
             <MudDivider Class="cut-detail-divider" />
@@ -162,13 +168,14 @@ else
                     }
                 </div>
             }
-            }
+            </div>
         </BodyContent>
     </ReleaseDetailScaffold>
+    </div>
 }
 
 @code {
-    [CascadingParameter] public IStreamingPlayerService? PlayerService { get; set; }
+    // PlayerService is cascaded by CutDetailBase (used there for the Theater release-playing predicate).
     [CascadingParameter] public IQueueService? Queue { get; set; }
 
     // Header Play: load the full album into the queue starting at track 0.