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.

DeepDrftModels/DTOs/WaveformProfileDto.cs

@@ -0,0 +1,14 @@
+namespace DeepDrftModels.DTOs;
+
+/// <summary>
+/// Wire contract for a stored waveform loudness profile. <see cref="Data"/> is the base64
+/// encoding of a <c>byte[BucketCount]</c>, each byte a peak-normalized loudness value in
+/// [0, 255] (the quantized form of a [0, 1] float). The frontend renders these as bar heights
+/// in the WaveformSeeker. A track with no stored profile yields no DTO (the frontend falls
+/// back to a flat seekbar), so this type never represents "absent" — only a present profile.
+/// </summary>
+public class WaveformProfileDto
+{
+    public int BucketCount { get; set; }
+    public string Data { get; set; } = string.Empty;
+}