fix(visualizer): lift zoom slider out of fixed backdrop's stacking context so it receives pointer events again (P10 W1)

DeepDrftPublic.Client/Controls/MixWaveformVisualizer.razor

@@ -9,20 +9,25 @@
 
 <div class="mix-waveform-bg">
     <canvas @ref="_canvas" class="mix-waveform-canvas"></canvas>
-
-    @* Viewing control only — never a seek surface. Hidden until a datum is present. *@
-    @if (_hasDatum)
-    {
-        <div class="mix-waveform-zoom">
-            <MudSlider T="double"
-                       Value="@ZoomFraction"
-                       ValueChanged="@OnZoomFractionChanged"
-                       Min="0"
-                       Max="1"
-                       Step="0.001"
-                       Size="Size.Small"
-                       Color="Color.Primary"
-                       aria-label="Waveform zoom" />
-        </div>
-    }
 </div>
+
+@* Viewing control only — never a seek surface. Hidden until a datum is present.
+   Deliberately a SIBLING of .mix-waveform-bg, not a child: the backdrop is position:fixed and so
+   forms its own stacking context, which would trap any descendant below the page's z-index:1
+   foreground (.mix-detail-foreground) and let that foreground swallow the slider's pointer events.
+   As a top-level sibling with its own z-index, the slider stacks above the foreground and stays
+   draggable. *@
+@if (_hasDatum)
+{
+    <div class="mix-waveform-zoom">
+        <MudSlider T="double"
+                   Value="@ZoomFraction"
+                   ValueChanged="@OnZoomFractionChanged"
+                   Min="0"
+                   Max="1"
+                   Step="0.001"
+                   Size="Size.Small"
+                   Color="Color.Primary"
+                   aria-label="Waveform zoom" />
+    </div>
+}