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/Services/AudioPlayerService.cs

@@ -33,6 +33,9 @@ public abstract class AudioPlayerService : IPlayerService, IAsyncDisposable
     /// </summary>
     public TrackDto? CurrentTrack { get; protected set; }
 
+    /// <inheritdoc />
+    public double[]? WaveformProfile { get; protected set; }
+
     // Events
     public EventCallback? OnStateChanged { get; set; }
     public EventCallback? OnTrackSelected { get; set; }

DeepDrftPublic.Client/Services/IPlayerService.cs

@@ -19,6 +19,14 @@ public interface IPlayerService
     string? ErrorMessage { get; }
     TrackDto? CurrentTrack { get; }
 
+    /// <summary>
+    /// Normalized loudness profile for the current track, each value in [0, 1], or null when no
+    /// profile is available (no track loaded, or the track has no stored profile). The seek zone
+    /// renders this as a waveform; a null profile drives the flat-but-seekable fallback. Fetched on
+    /// track select and cleared on unload/stop; <see cref="StateChanged"/> fires once it arrives.
+    /// </summary>
+    double[]? WaveformProfile { get; }
+
     // Events for UI updates
     EventCallback? OnStateChanged { get; set; }
     EventCallback? OnTrackSelected { get; set; }

DeepDrftPublic.Client/Services/StreamingAudioPlayerService.cs

@@ -77,6 +77,11 @@ public class StreamingAudioPlayerService : AudioPlayerService, IStreamingPlayerS
         // Create new cancellation token for this streaming operation
         _streamingCancellation = new CancellationTokenSource();
 
+        // Fetch the waveform profile alongside the audio. Fire-and-forget against the same
+        // streaming token so a track switch abandons it; it only updates display state and must
+        // never gate or fail the audio load (a missing profile yields the flat-seekbar fallback).
+        _ = LoadWaveformProfileAsync(track.EntryKey, _streamingCancellation.Token);
+
         try
         {
             // Set state to indicate loading has started
@@ -152,6 +157,67 @@ public class StreamingAudioPlayerService : AudioPlayerService, IStreamingPlayerS
         }
     }
 
+    /// <summary>
+    /// Fetches and decodes the track's waveform loudness profile, then notifies state so the
+    /// seek zone re-renders with real bars. Best-effort: a 404 (no stored profile) or any other
+    /// failure simply leaves <see cref="AudioPlayerService.WaveformProfile"/> null, which the
+    /// WaveformSeeker renders as a flat-but-seekable fallback. Never throws into the load path.
+    /// </summary>
+    private async Task LoadWaveformProfileAsync(string entryKey, CancellationToken cancellationToken)
+    {
+        WaveformProfile = null;
+
+        try
+        {
+            var result = await _trackMediaClient.GetWaveformProfileAsync(entryKey, cancellationToken);
+            if (cancellationToken.IsCancellationRequested) return;
+
+            if (result.Success && result.Value is { } dto)
+            {
+                WaveformProfile = DecodeWaveformProfile(dto);
+                await NotifyStateChanged();
+            }
+        }
+        catch (OperationCanceledException)
+        {
+            // Track switched or stopped before the profile arrived — nothing to surface.
+        }
+        catch (Exception ex)
+        {
+            // A failed profile fetch must not disturb playback; log and fall back to flat bars.
+            _logger.LogDebug(ex, "Failed to load waveform profile for {EntryKey}", entryKey);
+        }
+    }
+
+    /// <summary>
+    /// Decodes a <see cref="WaveformProfileDto"/> (base64 of byte[BucketCount], each 0..255) into
+    /// a normalized double[] in [0, 1]. Returns null if the payload is malformed so callers treat
+    /// it as "no profile" rather than rendering garbage bars.
+    /// </summary>
+    private static double[]? DecodeWaveformProfile(WaveformProfileDto dto)
+    {
+        if (string.IsNullOrEmpty(dto.Data)) return null;
+
+        byte[] bytes;
+        try
+        {
+            bytes = Convert.FromBase64String(dto.Data);
+        }
+        catch (FormatException)
+        {
+            return null;
+        }
+
+        if (bytes.Length == 0) return null;
+
+        var profile = new double[bytes.Length];
+        for (var i = 0; i < bytes.Length; i++)
+        {
+            profile[i] = bytes[i] / 255.0;
+        }
+        return profile;
+    }
+
     private async Task StreamAudioWithEarlyPlayback(TrackMediaResponse audio, CancellationToken cancellationToken)
     {
         byte[]? buffer = null;
@@ -438,6 +504,7 @@ public class StreamingAudioPlayerService : AudioPlayerService, IStreamingPlayerS
         LoadProgress = 0;
         ErrorMessage = null;
         CurrentTrack = null;
+        WaveformProfile = null;
 
         // 4. Reset streaming-specific state
         IsStreamingMode = false;