Added manga data and pipeline.

MangaReader.Core/Data/MangaCover.cs

@@ -0,0 +1,14 @@
+namespace MangaReader.Core.Data;
+
+public class MangaCover
+{
+    public int MangaCoverId { get; set; }
+
+    public int MangaId { get; set; }
+    public required Manga Manga { get; set; }
+
+    public required Guid Guid { get; set; }
+    public required string FileExtension { get; set; }
+    public string? Description { get; set; }
+    public bool IsPrimary { get; set; }
+}