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

feat(emailer): add Postmark and Resend providers

backend/Modules/Messaging/Handlers/GetMessageCount.cs

@@ -0,0 +1,44 @@
+using Hutopy.Modules.Messaging.Data;
+
+namespace Hutopy.Modules.Messaging.Handlers;
+
+public sealed class GetMessageCountRequest
+{
+    public Guid SubjectId { get; set; }
+    [BindFrom("page_size")] public int PageSize { get; set; } = 1000;
+}
+
+public record struct GetMessageCountResponse
+{
+    public required int Count { get; init; }
+}
+
+public class GetMessageCount(
+    MessagingDbContext context)
+    : Endpoint<GetMessageCountRequest, GetMessageCountResponse>
+{
+    public override void Configure()
+    {
+        Get("/api/messages/{SubjectId:guid}/count");
+        Options(o => o.WithTags("Messages"));
+        AllowAnonymous();
+    }
+
+    public override async Task HandleAsync(
+        GetMessageCountRequest req,
+        CancellationToken ct)
+    {
+        var messageCount = await context.GetMessageCountAsync(
+            req.SubjectId,
+            null,
+            req.PageSize,
+            ct);
+        
+        await SendAsync(
+            new()
+            {
+                Count = messageCount
+            },
+            cancellation: ct);
+    }
+}