many fixes and improvements - rework for modules/ and common/

feat(emailer): add Postmark and Resend providers

backend/Modules/Contents/Data/Album.cs

@@ -0,0 +1,11 @@
+using System.ComponentModel.DataAnnotations;
+using Hutopy.Common.Domain;
+
+namespace Hutopy.Modules.Contents.Data;
+
+public class Album : Entity
+{
+    public bool IsDeleted { get; private set; }   // private set → EF updates it
+    [MaxLength(255)] public required string Title { get; set; }
+    public IList<AlbumPhoto> Photos { get; set; } = new List<AlbumPhoto>();
+}