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

feat(emailer): add Postmark and Resend providers

backend/Modules/Contents/Data/AlbumPhoto.cs

@@ -0,0 +1,15 @@
+using System.ComponentModel.DataAnnotations;
+using Hutopy.Common.Domain;
+
+namespace Hutopy.Modules.Contents.Data;
+
+public class AlbumPhoto : Entity
+{
+    public bool IsDeleted { get; private set; } // private set → EF updates it
+    public Guid AlbumId { get; set; }
+    public Album Album { get; init; } = null!;
+    [MaxLength(2048)] public required string OriginalUrl { get; set; }
+    [MaxLength(2048)] public required string ThumbnailUrl { get; set; }
+    [MaxLength(256)] public string? Caption { get; set; }
+    public int Order { get; set; }
+}