feat(audio): add MP3 and FLAC upload support via format-routed processors

AudioProcessorRouter dispatches by extension; vault stores original bytes with correct MIME type.

DeepDrftContent/Processors/AudioProcessorRouter.cs

@@ -0,0 +1,42 @@
+using DeepDrftContent.FileDatabase.Models;
+
+namespace DeepDrftContent.Processors;
+
+/// <summary>
+/// Dispatches an audio file to the correct format processor by extension. The single seam through
+/// which <see cref="TrackContentService"/> processes uploads, so callers depend on one abstraction
+/// rather than three concrete processors.
+/// </summary>
+public class AudioProcessorRouter
+{
+    private readonly AudioProcessor _wavProcessor;
+    private readonly Mp3AudioProcessor _mp3Processor;
+    private readonly FlacAudioProcessor _flacProcessor;
+
+    public AudioProcessorRouter(
+        AudioProcessor wavProcessor,
+        Mp3AudioProcessor mp3Processor,
+        FlacAudioProcessor flacProcessor)
+    {
+        _wavProcessor = wavProcessor;
+        _mp3Processor = mp3Processor;
+        _flacProcessor = flacProcessor;
+    }
+
+    /// <summary>
+    /// Processes <paramref name="filePath"/> with the processor matching its extension, returning an
+    /// <see cref="AudioBinary"/> carrying the stored bytes and extracted metadata. Throws
+    /// <see cref="ArgumentException"/> for unsupported extensions.
+    /// </summary>
+    public async Task<AudioBinary?> ProcessAudioFileAsync(string filePath)
+    {
+        var ext = Path.GetExtension(filePath).ToLowerInvariant();
+        return ext switch
+        {
+            ".wav" => await _wavProcessor.ProcessWavFileAsync(filePath),
+            ".mp3" => await _mp3Processor.ProcessMp3FileAsync(filePath),
+            ".flac" => await _flacProcessor.ProcessFlacFileAsync(filePath),
+            _ => throw new ArgumentException($"Unsupported audio format: {ext}", nameof(filePath)),
+        };
+    }
+}