Add server-side waveform loudness profiling on track upload

ILoudnessAlgorithm strategy (RmsLoudnessAlgorithm first impl), WaveformProfileService
stores quantized byte[] sidecar in new MediaFileVault (profiles vault), wired into
UnifiedTrackService.UploadAsync; failure is logged and swallowed. WaveformProfileDto
and WaveformProfileOptions in shared projects.

DeepDrftContent/Processors/WaveformProfileService.cs

@@ -0,0 +1,123 @@
+using DeepDrftContent.Constants;
+using DeepDrftContent.FileDatabase.Models;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using FileDb = DeepDrftContent.FileDatabase.Services.FileDatabase;
+
+namespace DeepDrftContent.Processors;
+
+/// <summary>
+/// Computes a track's waveform loudness profile from its WAV bytes and persists it as a sidecar
+/// in the <see cref="VaultConstants.WaveformProfiles"/> vault, keyed by the track's EntryKey.
+/// The profile is the upload-time, off-the-playback-path representation the frontend fetches to
+/// render the WaveformSeeker. The loudness measure is injected (<see cref="ILoudnessAlgorithm"/>)
+/// so it can be swapped without changing storage or the wire format.
+/// </summary>
+public class WaveformProfileService
+{
+    private const string ProfileExtension = ".wfp";
+
+    private readonly FileDb _fileDatabase;
+    private readonly AudioProcessor _audioProcessor;
+    private readonly ILoudnessAlgorithm _loudnessAlgorithm;
+    private readonly WaveformProfileOptions _options;
+    private readonly ILogger<WaveformProfileService> _logger;
+
+    public WaveformProfileService(
+        FileDb fileDatabase,
+        AudioProcessor audioProcessor,
+        ILoudnessAlgorithm loudnessAlgorithm,
+        IOptions<WaveformProfileOptions> options,
+        ILogger<WaveformProfileService> logger)
+    {
+        _fileDatabase = fileDatabase;
+        _audioProcessor = audioProcessor;
+        _loudnessAlgorithm = loudnessAlgorithm;
+        _options = options.Value;
+        _logger = logger;
+    }
+
+    /// <summary>
+    /// Computes the loudness profile from <paramref name="wavBytes"/> and stores it under
+    /// <paramref name="entryKey"/>. Returns false (and logs) on any failure — a missing profile
+    /// is handled gracefully downstream, so callers on the upload path log-and-continue rather
+    /// than failing the upload. Does not throw for expected failure modes.
+    /// </summary>
+    public async Task<bool> ComputeAndStoreAsync(ReadOnlyMemory<byte> wavBytes, string entryKey)
+    {
+        try
+        {
+            var pcm = _audioProcessor.TryExtractPcm(wavBytes.Span);
+            if (pcm is null)
+            {
+                _logger.LogWarning(
+                    "Waveform profile not computed for {EntryKey}: WAV PCM could not be extracted.",
+                    entryKey);
+                return false;
+            }
+
+            var value = pcm.Value;
+            var profile = _loudnessAlgorithm.Compute(
+                value.Pcm.Span,
+                value.Channels,
+                value.SampleRate,
+                value.BitsPerSample,
+                _options.BucketCount);
+
+            var quantized = Quantize(profile);
+
+            await EnsureVaultAsync();
+
+            var binary = new MediaBinary(new MediaBinaryParams(quantized, quantized.Length, ProfileExtension));
+            var stored = await _fileDatabase.RegisterResourceAsync(
+                VaultConstants.WaveformProfiles, entryKey, binary);
+
+            if (!stored)
+            {
+                _logger.LogWarning("Waveform profile vault write failed for {EntryKey}.", entryKey);
+                return false;
+            }
+
+            return true;
+        }
+        catch (Exception ex) when (ex is not OperationCanceledException)
+        {
+            _logger.LogError(ex, "Waveform profile computation failed for {EntryKey}.", entryKey);
+            return false;
+        }
+    }
+
+    /// <summary>
+    /// Returns the stored quantized profile bytes for a track, or null if no profile is stored
+    /// (existing tracks predate profiling, and computation may have failed). Each byte is a
+    /// peak-normalized loudness value in [0, 255].
+    /// </summary>
+    public async Task<byte[]?> GetProfileAsync(string entryKey)
+    {
+        var binary = await _fileDatabase.LoadResourceAsync<MediaBinary>(
+            VaultConstants.WaveformProfiles, entryKey);
+        return binary?.Buffer;
+    }
+
+    /// <summary>
+    /// Maps each [0, 1] bucket to a [0, 255] byte. 1.0 maps to 255; the multiply-by-255 with a
+    /// truncating cast keeps every in-range value within a byte without a clamp branch.
+    /// </summary>
+    private static byte[] Quantize(double[] profile)
+    {
+        var bytes = new byte[profile.Length];
+        for (var i = 0; i < profile.Length; i++)
+        {
+            bytes[i] = (byte)(profile[i] * 255);
+        }
+        return bytes;
+    }
+
+    private async Task EnsureVaultAsync()
+    {
+        if (!_fileDatabase.HasVault(VaultConstants.WaveformProfiles))
+        {
+            await _fileDatabase.CreateVaultAsync(VaultConstants.WaveformProfiles, MediaVaultType.Media);
+        }
+    }
+}