refactor: standardize project names to Musify.* and flatten layout

- Flatten nested per-repo folders into flat Musify.* projects at root
- Rename assemblies/csproj: Domain->Musify.Domain, Application->Musify.Application,
  Infrastructure->Musify.Infrastructure, WebApi->Musify.Api, Worker->Musify.Worker,
  StreamingGateway->Musify.StreamingGateway
- Rename WebApi.* namespaces to Musify.Api.*
- Update all ProjectReference paths and the solution file
- Consolidate stray per-repo dotfiles; add root .gitattributes
- Move flutter client out to _archive

Musify.Infrastructure/Configuration/AudioTranscoderConfiguration.cs

@@ -0,0 +1,41 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace Musify.Infrastructure.Configuration
+{
+    public class AudioTranscoderConfiguration
+    {
+        public const string SectionName = "AudioTranscoder";
+
+        [Required]
+        public TimeSpan TranscodingTimeout { get; set; } = TimeSpan.FromMinutes(5);
+
+        [Required]
+        public FfmpegConfiguration Ffmpeg { get; set; } = new FfmpegConfiguration();
+    }
+
+    public class FfmpegConfiguration
+    {
+        [Required]
+        public string ExecutableName { get; set; } = "ffmpeg";
+
+        [Required]
+        public string OutputFileName { get; set; } = "audio.m4a";
+
+        [Required]
+        public string AudioCodec { get; set; } = "aac";
+
+        [Required]
+        public string AudioBitrate { get; set; } = "128k";
+
+        [Range(1, 8)]
+        public int AudioChannels { get; set; } = 2;
+
+        [Range(8000, 192000)]
+        public int AudioSampleRate { get; set; } = 48000;
+
+        [Required]
+        public string AudioProfile { get; set; } = "aac_low";
+
+        public string AdditionalArguments { get; set; } = string.Empty;
+    }
+}