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/WaveformSeeker.razor

@@ -0,0 +1,45 @@
+@namespace DeepDrftPublic.Client.Controls.AudioPlayerBar
+
+@* High-density loudness-waveform seekbar. Replaces the MudSlider in PlayerSeekZone.
+   Bars render once; the played/unplayed split is a single clip-width animation on the
+   muted overlay (see .razor.css), so a seek never re-renders the 200 bar divs. *@
+<div class="@($"waveform-seeker {Class}".TrimEnd())"
+     style="--played-fraction: @PlayedFraction.ToString("F4", System.Globalization.CultureInfo.InvariantCulture);"
+     @ref="_seekerElement"
+     @onpointerdown="HandlePointerDown"
+     @onpointermove="HandlePointerMove"
+     @onpointerup="HandlePointerUp"
+     @onpointercancel="HandlePointerUp"
+     @onpointerleave="HandlePointerLeave">
+
+    @* Played layer: every bar in the accent colour. *@
+    <div class="waveform-layer waveform-layer-played">
+        @for (var i = 0; i < _renderedBars.Length; i++)
+        {
+            <div class="waveform-bar" style="--bar-height: @FormatHeight(_renderedBars[i]);"></div>
+        }
+    </div>
+
+    @* Unplayed overlay: an identical bar set in the muted colour, clipped to the
+       unplayed portion. Only its clip width changes on seek — one CSS property. *@
+    <div class="waveform-layer waveform-layer-unplayed">
+        @for (var i = 0; i < _renderedBars.Length; i++)
+        {
+            <div class="waveform-bar" style="--bar-height: @FormatHeight(_renderedBars[i]);"></div>
+        }
+    </div>
+
+    @* Playhead rule at the split point. *@
+    <div class="waveform-playhead"></div>
+
+    @* Hover preview line + time tooltip (suppressed while dragging). *@
+    @if (_showHover && !_isSeeking)
+    {
+        <div class="waveform-hover-line"
+             style="left: @_hoverFraction.ToString("P2", System.Globalization.CultureInfo.InvariantCulture);"></div>
+        <div class="waveform-hover-time"
+             style="left: @_hoverFraction.ToString("P2", System.Globalization.CultureInfo.InvariantCulture);">
+            @FormatTime(_hoverTime)
+        </div>
+    }
+</div>