fix(theater): replace max-height collapse with grid-rows + visibility; fix keyboard-focus leak when collapsed

DeepDrftPublic.Client/Pages/SessionDetail.razor

@@ -72,6 +72,7 @@ else
            collapsing wrapper so they do not pop — collapsed to zero height when Theater is on AND this
            Session is the playing release. The top row above stays. OFF eases this region back in. *@
         <div class="dd-theater-collapsible @(IsContentHidden ? "dd-theater-collapsed" : null)">
+        <div class="dd-theater-collapsible-inner">
         @* The overlay shows the cover thumbnail only when it differs from the resolved hero image —
            when there is no dedicated hero, heroImage already falls back to release.ImagePath, so the
            thumb would duplicate the background. That logic lives in ReleaseHeroOverlay. *@
@@ -98,6 +99,7 @@ else
 
         <ReleaseDescription Description="@release.Description" />
         </div>
+        </div>
 
     </MudContainer>
 }