Replace MudSlider seekbar with WaveformSeeker loudness-waveform control

DOM bar chart with clip-overlay progress split; pointer-capture drag;
WaveformProfile fetched on load (fire-and-forget, cancellable); flat
fallback when no profile; small lazily-loaded waveformSeeker.js for
getBoundingClientRect and setPointerCapture.

DeepDrftPublic.Client/Controls/AudioPlayerBar/PlayerSeekZone.razor

@@ -1,18 +1,9 @@
 @namespace DeepDrftPublic.Client.Controls.AudioPlayerBar
 
 <MudStack Row="false" Spacing="0" Class="@Class">
-    <div class="mx-3"
-         @onpointerdown="HandlePointerDown"
-         @onpointerup="HandlePointerUp"
-         @onpointerleave="HandlePointerLeave">
-        <MudSlider T="double"
-                   Min="0"
-                   Max="@(Duration ?? 0D)"
-                   Step="0.1"
-                   Value="@DisplayTime"
-                   ValueChanged="HandleValueChanged"
-                   Immediate="true"
-                   Disabled="@(!CanSeek)"/>
-    </div>
+    <WaveformSeeker OnSeekStart="OnSeekStart"
+                    OnSeekChange="OnSeekChange"
+                    OnSeekEnd="OnSeekEnd"
+                    Class="seek-waveform"/>
     <TimestampLabel CurrentTime="DisplayTime" Duration="@Duration"/>
 </MudStack>