Anchor ambient visualizer to viewport bottom; occlude via z-index not clip

Drop the --player-height bottom inset so the fixed visualizer fills the
viewport; the inset player bar no longer leaves a page-background gap. The
spacer now occludes via opaque page-surface + z-index. Visualizer no longer
reads --player-height, so spacer.ts coalescing is removed.

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

@@ -36,10 +36,9 @@ public partial class AudioPlayerBar : ComponentBase, IAsyncDisposable
     // error banner.
     //
     // _miniDock is the minimized FAB container. We observe it in minimized state so
-    // --player-height stays non-zero (the FAB's actual height) and the WaveformVisualizer
-    // clips to the top of the FAB rather than extending to the viewport bottom (fix §1).
-    // The player-spacer's .minimized class uses a hardcoded 60px and ignores the var,
-    // so publishing the FAB height here does not regress the spacer.
+    // --player-height stays non-zero (the FAB's actual height). The player-spacer's
+    // .minimized class uses a hardcoded 60px and ignores the var, so this is belt-and-
+    // braces; the var's sole live consumer is the spacer's .expanded height.
     private ElementReference _playerRoot;
     private ElementReference _miniDock;
     private ElementReference _lastObservedElement;