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

feat(emailer): add Postmark and Resend providers

backend/Infrastructure/Security/MissingClaimException.cs

@@ -0,0 +1,5 @@
+namespace Hutopy.Infrastructure.Security;
+
+public class MissingClaimException(
+    string claimName)
+    : Exception($"Claim '{claimName}' is missing.");