feat(album): add cover picture functionality to albums and enhance album management API

Models/Request/Album/AlbumUpdateRequest.cs

@@ -0,0 +1,15 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace Foxel.Models.Request.Album
+{
+    public class AlbumUpdateRequest
+    {
+        [StringLength(100, ErrorMessage = "相册名称长度不能超过100个字符")]
+        public string? Name { get; set; }
+
+        [StringLength(500, ErrorMessage = "相册描述长度不能超过500个字符")]
+        public string? Description { get; set; }
+
+        public int? CoverPictureId { get; set; }
+    }
+}