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/FileDatabase/Services/MediaVault.cs

@@ -219,6 +219,32 @@ public class AudioVault : MediaVault
     }
 }
 
+/// <summary>
+/// Concrete vault for plain <see cref="MediaBinary"/> entries (vault type
+/// <see cref="MediaVaultType.Media"/>) — bytes plus an extension, no audio/image-specific
+/// metadata. Used for sidecar artifacts such as waveform loudness profiles. The base
+/// <see cref="MediaVault"/> already handles Media-typed storage via the registry; this only
+/// provides the concrete factory the Image and Audio vaults also provide.
+/// </summary>
+public class MediaFileVault : MediaVault
+{
+    private MediaFileVault(string rootPath, VaultIndex index, IndexFactoryService? factoryService = null)
+        : base(rootPath, index, factoryService) { }
+
+    public static async Task<MediaFileVault?> FromAsync(string rootPath, IndexFactoryService? factoryService = null)
+    {
+        var factory = factoryService ?? new IndexFactoryService();
+        var index = await factory.LoadOrCreateVaultIndexAsync(rootPath, MediaVaultType.Media);
+
+        if (index != null)
+        {
+            return new MediaFileVault(rootPath, (VaultIndex)index, factory);
+        }
+
+        return null;
+    }
+}
+
 /// <summary>
 /// An open read-only stream over a vault entry plus the extension needed to
 /// resolve its MIME type. Caller owns the stream and must dispose it.