feat(background): add visual recognition task and refactor picture processing

Models/DataBase/BackgroundTask.cs

@@ -7,6 +7,7 @@ namespace Foxel.Models.DataBase
     public enum TaskType
     {
         PictureProcessing = 0,
+        VisualRecognition = 1,
     }
 
     public enum TaskExecutionStatus

Models/DataBase/Picture.cs

@@ -9,8 +9,16 @@ public class Picture : BaseModel
 {
     [StringLength(255)] public string Name { get; set; } = string.Empty;
 
+    /// <summary>
+    /// Path to the high-definition (possibly format-converted) image.
+    /// </summary>
     [StringLength(1024)] public string Path { get; set; } = string.Empty;
 
+    /// <summary>
+    /// Path to the original, untouched uploaded file.
+    /// </summary>
+    [StringLength(1024)] public string OriginalPath { get; set; } = string.Empty;
+
     [StringLength(1024)] public string? ThumbnailPath { get; set; } = string.Empty;
 
     [StringLength(2000)] public string Description { get; set; } = string.Empty;