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

feat(emailer): add Postmark and Resend providers

backend/Modules/Contents/Models/FollowModel.cs

@@ -0,0 +1,7 @@
+namespace Hutopy.Modules.Contents.Models;
+
+[PublicAPI]
+public record FollowModel(
+    Guid CreatorId,
+    string CreatorName,
+    string? CreatorPortraitUrl);