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

feat(emailer): add Postmark and Resend providers

backend/Modules/Messaging/Handlers/AddMessage.cs

@@ -0,0 +1,55 @@
+using Hutopy.Infrastructure.Security;
+using Hutopy.Modules.Messaging.Data;
+
+namespace Hutopy.Modules.Messaging.Handlers;
+
+[PublicAPI]
+public sealed class AddMessageRequest
+{
+    public Guid? Id { get; set; }
+    public required Guid SubjectId { get; set; }
+    public required string Message { get; set; }
+}
+
+internal sealed class AddMessageRequestValidator
+    : Validator<AddMessageRequest>
+{
+    public AddMessageRequestValidator()
+    {
+        RuleFor(r => r.SubjectId)
+            .NotNull().WithMessage("You must specify a SubjectId")
+            .NotEmpty().WithMessage("You must specify a non-empty SubjectId");
+
+        RuleFor(r => r.Message)
+            .NotNull().WithMessage("You must specify a Message")
+            .NotEmpty().WithMessage("You must specify a non-empty Message");
+    }
+}
+
+public class AddMessage(
+    MessagingDbContext context)
+    : Endpoint<AddMessageRequest>
+{
+    public override void Configure()
+    {
+        Post("/api/messages");
+        Options(o => o.WithTags("Messages"));
+    }
+
+    public override async Task HandleAsync(
+        AddMessageRequest req,
+        CancellationToken ct)
+    {
+        var message = new Message
+        {
+            Id = req.Id ?? Guid.CreateVersion7(),
+            SubjectId = req.SubjectId,
+            CreatedBy = User.GetUserId(),
+            Value = req.Message
+        }; 
+        
+        await context.Messages.AddAsync(message, ct);
+
+        await context.SaveChangesAsync(ct);
+    }
+}