Refactor downloads to use job-specific subdirectories

Organize downloaded files into per-job subdirectories under "downloads" instead of a flat structure. Update DownloadController and VideoService to read, write, and delete files within these job-specific directories. Add helper methods for directory management and improve logging. Update download/delete endpoints and result URLs to reflect the new structure. Clean up empty job directories after file deletion.

TuneRipper.Shared/Models/ProcessVideoModels.cs

@@ -5,6 +5,7 @@ public class ProcessVideoRequest
     public string? Url { get; set; }
     public string? Format { get; set; } = "mp3";
     public string? Quality { get; set; } = "128";
+    public string? SessionId { get; set; } // Add session ID support
 }
 
 public class ProcessVideoResponse
@@ -14,6 +15,7 @@ public class ProcessVideoResponse
     public string? FileName { get; set; }
     public string? DownloadUrl { get; set; }
     public YouTubeVideoDetails? VideoDetails { get; set; }
+    public string? SessionId { get; set; } // Include session ID in response
 }
 
 public class DownloadProgress